I was looking into making one of these a couple years ago, and I think it's about time I do it. You make this alcohol stove out of two 12 oz Heineken keg cans and one soda can. 40 ml of alcohol will bring a quart of water to boil in 8 minutes.
Here's the alcohol stove: http://www.csun.edu/~mjurey/pennywood.html
Directions for making it: http://www.csun.edu/~mjurey/stoveinstruct.html
I was happy to find that they now also have a little wood burning stove. It looks really easy to make, using just a 4" diameter can and 3 tent stakes. A couple handfuls of pencil sized sticks will bring a quart of water to boil in 10 minutes and keep it at a boil for 5 to 10 minutes more (or indefinitely if you keep adding sticks).
Here's another easy to make super lightweight stove that uses Esbit fuel tablets. It would be good in a pinch, but the problem would be finding more fuel tablets if SHTF.
I thought some people here may find this useful. It would be good for a bugout bag, or any emergency situation where you need to boil water or cook some food.