1. an empty soda can for the pot some other type of can like a veggie can and
2. a few sheets of toilet paper, paper towel, cardboard or other absorbent material, including sand. (...but no synthetics!)
3. a level, flat and fireproof surface (or a second empty can of approximately the same diameter as the pot can or a little larger - preferably with a bottom that will fit or accept the soda can bottom nicely - see photos).
4. a fire starter of some type, like book matches or a sparker, to light the fuel
5. 91% Isopropyl alcohol. 70% may work directly and if not can be "salted out.". Fuels that float on water are not recommended.
6. provision for venting of exhaust fumes and allowing intake of fresh air if used in a confined space such as inside a car.
I used 91% Isopropyl alcohol for fuel since I always carry a little with me in a spray bottle to kill germs after shaking hands, and as fuel for the laminar or pressure can stoves I carried with me in case I was overcome by the ultralight backpacking urge. This personal pocket stove, however, (except for the weigh of the fuel) is so light it will even support super ultralight backpacking!
All alcohol fuels should work if the proof is high enough. Even kerosene or jet fuel might work (in case you are in an airplane accident) but the stoichiometric ratio will be lower, i.e. lots of soot. I would not resort to gasoline or other highly volatile, high energy fuels due to the low temperature of combustion, unless you have absolutely no other choice. In any case the pot you use with high energy fuels should be made of steel, even if filled with water, rather than aluminum.
If you anticipate having only gasoline available in such an emergency (from your car's tank) look for stove designs intended for use with highly volatile and high energy fuels. Warning: fuels other than alcohol such as gasoline may burn hot enough to melt aluminum while fuels like oil or mineral spirits may produce an unacceptable amount of carbon monoxide and soot, with this design.
Also, DO NOT REMOVE POT FROM STOVE UNTIL THE FLAME GOES OUT WITHOUT A SECURE (WEIGHTED) INTERMEDIATE STOVE COVER SUCH AS A STEEL CAN TOP OR YOU MAY HAVE TO DEAL WITH A FLARE UP BY IMMEDIATELY RETURNING THE POT TO THE STOVE.
Step 1: Put it together
With a flat, fireproof surface all you need do is cut or tear 10 to 30 sheets of material the thickness of tissue, for a total thicknes of 1/4" to 3/8", to a diameter a bit larger than the can you will be using for a pot.
Soak these sheets in fuel and place on the flat, fireproof surface.
Place the pot with water to boil (or perhaps a can of vegetables or soup) on top of these sheets and then light the sheets under the pot around the edges.
If you have a second empty can suitable for supporting the pot and very close to the same diameter, turn it upside down and place the soaked sheets over the bottom. Then place the pot on top of the sheets and light the edges. A veggie can on bottom with a soda can on top worked really well for me.
A ring of blue flame should surround the pot and then the pot should begin heating it up.
if the fuel burns up before the desired temperature is reached, no problem. Just remove the pot, replenish the fuel and put the pot back on followed by relighting.
WARNING: Be absolutely sure to replenish the fuel, only after the flame is extinguished - (repeat after me: ...only after the flame is out!).
Be sure the fire is out! Accidents can happen quickly, especially when replenishing fuel. Burns can disable or disfigure permanently. Do not take any chance!
I've tried modifications to increase fuel capacity and to produce higher temperatures but these go beyond what is actually necessary in an emergency.
For testing though you might want to use and empty cold cream jar to store your fuel soaked absorbent material - even use it to be pre-prepared in the event of an emergency.