There are situations where the difference between a hot meal and a cold one is literally life and death. A hot meal can stave off hypothermia, and bringing food to boiling can prevent disease. Fire is good, and using fire to cook is better.
I used to do a lot of camping and hiking, and have vague ambitions of returning to those pursuits. Because of that, and because I like having alternate means for important resources, over the past year I have been doing a lot of research into methods of heating food and drinks when away from utilities... or when utilities fail.
This was brought home to me, personally, during a recent five hour blackout which hit my county and two adjacent. Adding to the problems the situation caused, this was late on a very cold Winter night.
My neighborhood has long had problems with the electrical supply. Things are much better now, since the utility company came through and upgraded much of the equipment a few years ago. However, we still have brief blackouts - usually only a few minutes - a couple of times a year, with occasional longer outages. This, though, was a record, in both duration and geographic extent.
Because of the recurring outages in my neighborhood, many people around here were well equipped with candles and kerosene heaters during the big blackout. However, I had candles, a pair of Aladdin kerosene mantle lamps, a natural gas mantle lamp rated for indoor use - mounted to a wall in the basement - a Kerosun kerosene heater (which doubles as a stove), and a neat little folding camp stove. I fueled the kerosene heater, put it on the basement floor and lit it. I also lit the natural gas mantle lamp. Upstairs, I had both kerosene lamps and four large candles going. Briefly, I also used the folding stove. When the power came back my upstairs temperature was still quite comfortable, having dropped only a few degrees in five hours on a very cold night.
Better, during that long outage, I was able to make a large mug of steaming hot tea. I put that camp stove on my kitchen range and used it to heat the water.
The folding stove - meant for camping and hiking - is made by Sterno. It's steel, so it's heavier than many folding stoves for the same use. However, it is sturdy, folds almost flat, and can be used with a wide variety of fuels. Using Sterno cans - there are some specifically intended for cooking, with a higher output than the tray warmers - it would still take quite a while to boil enough water for a bowl of soup or a mug of tea. However, the can holder in the bottom will also hold many other types of fuel containers. They can be found in many places, but the best prices I have located are on eBay. The stove usually comes with a couple of the Sterno camping fuel cans.
That cold, dark night I didn't use the Sterno cans. Instead, I used the fuel can for a very clever little stove made for the Swiss Army, the M71. It burns hotter, for longer, with a cleaner flame, than any other canned heat I've tried. It has a re-closeable lid, and when you first open it there's a thick aluminum seal you need to cut out. After use, simply put the cover back on. It comes with a springy steel sheet metal pot support which stores around the stove, and which in use fits in the groove inside the can's top lip.
The M71 when used as intended is quite secure, very light and compact, and it produces a lot of heat at a high rate from its gel fuel. Prices vary widely for these, so shop around. These stoves come plastic wrapped with fuel canister, spring steel stove and a book of matches. The only caveat I know of is that if the thick gel fuel has bubbles those will pop from the heat. The fuel is so thick I've never seen it spatter when this happens, but it might. Oh, and the instructions are in Swedish.
Why didn't I just use that little stove, instead of the the Sterno folding stove? Two reasons. First, the Sterno stove is much studier and more stable. Second, the folding stove holds the pot or pan higher above the flames, which allows more complete combustion. This reduces carbon monoxide production, and also fumes from unburned fuel.
Though the odor from the Swiss stuff is pretty mild, that doesn't hold true for all canned fuels. Some have noticeable odor, as do some solid fuels. Whether the odor will be objectionable to a particular individual depends on the person and how enclosed the space. (Speaking of odor, that was one reason I didn't heat the water for my tea on the Kerosun stove, with another being because it was too large to go easily on my kitchen range, and I didn't feel like squatting over it on the basement floor.)
Speaking of fuel, alcohol - either liquid or gelled - is very popular for hiking and camping stoves. (Many canned heating units used gelled alcohol, but what I mean here is the separate alcohol gel fuel.) The gelled alcohol fuel I've seen is military surplus, in little olive-drab packets with instructions on one side and pithy bits of advice regarding military life and operations on the other. The gel is so thick it takes a bit of effort to squeeze out, but it also stays where you put it, even when burning. You can use it in any stove designed for fuel tabs, and some designed for fuel cans. Note that many alcohol fuels produce very little visible flame, which can be a problem with liquid fuels. A bit of spilled liquid fuel from filling a stove which ignites might not be noticed until it sets fire to something, or burns the user.
There are two types of solid fuel tabs I have experience with, both developed for military use but today having civilian versions. One of these is the US military's trioxane. The other is the Esbit-type fuel tab. These - as well as the gel - burn vigorously, quickly bringing - as an example - a canteen cup of water to a boil. Both types have little odor (again, this will very by person and situation) leave little ash, and some formulations produce very little visible flame.
Other common fuels are Coleman/white gas (naphtha) and kerosene (for kerosene I am include a wide range of fuels, such as diesel and heater fuel, as well as dedicated lamp oil). Gasoline is rarely used, even though unleaded is no more dangerous than naphtha.
Kerosene, gasoline and naphtha have a bit higher energy density per unit mass and volume than the alcohols, but the difference is small. Surprisingly, the solid fuels have less energy than even alcohol per gram, though more per milliliter. Paraffin, beeswax and mixes are about the same as the more potent liquid fuels per gram, and more compact, but don't really burn vigorously enough for practical cooking.
There are many camping stoves out there, of a wide variety of designs and using a number of different fuels. There are even flameless heaters, which depend on adding water to make them rust very, very fast. I live alone, so a small, single-burner stove is enough for emergencies. If you have a large family you may need something like a Coleman two-burner pressure fed stove using naphtha (white gas). These cook quickly, and are adjustable so you can simmer or warm with good control. You do have to pump them, though, and pay attention to the pressure.
Gas canister stoves use low-density fuels such as butane and propane, or a mix, in pressurized cans. They are often lighter than pressurized liquid fuel stoves. They - like the pressure stoves - produce intense heat and are also adjustable, making cooking easier and more flexible. Many canister stoves are specifically rated for use inside tents. (Keep in mind that the carbon monoxide ratings for camping stoves are for very enclosed spaces, such as tents. Whether a stove unsafe for a small tent would be safe in a home is uncertain. Just remember that CO is lighter than air.)
The Zip Stove has the disadvantage that it uses batteries, to drive a forced air fan. However, it has a major advantage over most camping stoves in that it uses available materials - such as twigs and pine needles - for fuel. While wood has too low an energy density to be worth carrying with you, dry wood is readily available most places people hike and camp, and you could easily stockpile some at your home. The forced draft of the Zip Stove makes fires easy to start and hotter burning, speeding cooking. Once it gets going good, it will even burn damp materials.
There is a compromise in stove design between adequate ventilation and keeping wind from blowing the heat away. Some stoves handle this better than others. Another reason I like the Sterno folding stove is that it includes a moveable front flap which can be used to adjust the airflow. Normally it would be fully closed to direct the convective flow of air upwards and help reflect heat, but if things are cooking a bit to fast you can open this to adjust the heat. Note that this is not a very large adjustment without a some wind to defend against.
In the very small category there are things such as the Vargo Outdoors Triad titanium stove, which only burns alcohol, and the Triad xe, which burns alcohol or fuel tabs or gel. Both are available for under $30. The Triad is about the size and shape of a can of shoe polish, and very, very light. Unfold the three legs and the identical (except for being on the top instead of the bottom) pot supports, add fuel, light and cook. Note that while the stoves are very small and extremely light, you still need to carry the fuel for them.
I have one of the multi-fuel Triad xe units, and it's very interesting. There's a center puck - normally held in the tray by the folded pot holder stems - which is used with alcohol. For solid fuel tabs or gel alcohol, simply remove the puck, put the fuel in the tray, light and cook. Using alcohol requires a bit more work. You twist the puck apart, producing a small pan and a vented cover. Fill the pan with alcohol, put the cover back on, put the puck in the tray, pour a little alcohol onto the puck to prime it and light. If you've done it right, by the time the outside alcohol has burned away the inside alcohol is hot enough to produce vapor.
Some folks actually make their own stoves similar to the Triad from aluminum soda or beer cans. I'm not that eager to save a few dollars in exchange for aluminum cuts. (Ouch.)
The folding WetFire stove is even smaller. It comes in steel and titanium versions, with the latter being the lighter (and more expensive). It has three flanges riveted to the bottom of a small tray. The tray is just slightly bigger than a fuel tab. The flanges unfold, pivoting around the central rivet, to form both legs for the stove and a stand for a pot or cup.
Several armies have military canteen cup stoves. These serve as both stove and cooking stand, take fuel tabs or gel, and when not in use fit around the base of the issue canteen cup, which in turn fits around the bottom of the canteen. There are both military surplus and civilian versions available. The limitation of these is that they are generally shaped to securely fit the canteen cup and nothing else.
A more generally useful military-originated stove is the Esbit. There are many versions besides the original, with different mixes of good and bad points. For example, Coghlan's makes a version which isn't quite as sturdy as the Esbit, but comes with more fuel. The Esbit was originally a WWII German Army stove, and is still in use by several militaries. Again there are both military surplus and civilian models. When folded closed it will store enough fuel tabs to heat over half a liter of water, depending on starting temperature. Somewhat larger than a deck of cards closed, it unfolds to hold the burner pan off the ground and support a pot or pan high enough for generally good combustion with fuel tabs or gel. There are even disposable Esbit stoves, which come flat in a package with some fuel tabs. Just fold the heavy foil into shape, add tabs and light.
Coghlan's makes a folding stove which seems to be popular. It is cheaper than the Sterno folding stove, but is heavier, doesn't block the wind as well and is shorter, allowing less distance between flame source and flame target. It also comes painted, which baffles me. When you first use one of the Coghlan's stoves you smell the burned paint. Substantial use is required before enough of this burns off that you don't get the odor. The Sterno stove is scent-free. However, the Coghlan's stove has a burning tray which will hold canned heat, fuel tabs or gelled alcohol.
This short article barely scratches the surface of the topic. There's a huge variety of portable stoves out there, of many different brands, for any sort of cooking. Whether for hiking, cooking at a campground or preparing meals during an emergency; for yourself, your immediate family or your entire block; whether fancy or simple; there's something for everyone. Tailgate party-goers bring entire kitchens, including portable barbecue rigs. There are even portable electric stoves and ovens, if you have a generator or are at a campground with utilities. Prices range from literally $2.50 to hundreds of dollars. Everyone should have at least something for emergencies. As noted here, this doesn't have to be expensive or difficult.