Beer can stove, for when you should have listened to your girlfriend and brought a stove in the first place...

I had seen one of these made in a video once, making one in real life proved quite easy.

First step is the best - drink two beers (look for little "AL" sign on them, to make sure they're not laminate cans).

Then comes the somewhat harder part, you have to find a can with the same diameter as the rim of the beer can, red bull cans work, but are hard to drink... (try and pawn it of at a techno-party and have some vodka to go with it).

Cut the top of the two beer cans so that one is ~1.5 times as tall as the other. If you make a really tall one, you can cook longer before the fuel runs out, but it'll be more unstable as well. Try to cut really neatly. Now make evenly spaced holes (Ø<1mm) around the side of the tallest bottom part. In this same can take out the inner curved part that was the bottom of the beer can. Then cut the redbull can to the combined height of the two beer cans, when they're stuck fully into one another (this can be tricky).

After this you're good to go. Fill about 2/3 with ethanol and light through big centre opening. Let the stove heat up. When the ethanol is boiling put your desired pot on it, closing the top opening and forcing ethanol steam out the side "jets". This is the whole point of this stove design, as it preheats the fuel, and by only burning the ethanol steam in little jets, it makes sure the combustion is well oxygenated - hot stuff!

All well and good - it worked great in the kitchen, but real life has wind...
I resourced some metal and made a windscreen. If you need to do this, make sure there is no holes in it under the handle of your pot! (handle will melt)

And now, just add your favourite travel food to your trusted pot, and leave to simmer.
On a side note here, my girlfriend came up with a way of shortening cooking time for pasta/lentils/rice when you're on the trail. Simply put today dinner in a half litre bottle, fill with water, and leave it in your backpack until it's dinner time (works especially well for high altitude).