Another super easy stove to make is the supercat stove. This was easy to make (I figured it out), and, with the exception of the windscreen, they likely have all the stuff for making this lying around. In all seriousness, it took me about 15 minutes to make. And, it worked adequately the first time I used it. I since modified it a little (too much space within the windscreen), and have yet to test it. The first attempt got the water hot, but not boiling. My next attempt I hope to get it to a rolling boil.
This is my normal daypack stove: Supercat stove, made out of a cat food can, windscreen made out of aluminum flashing, with two wingnuts to hold it together, 2 aluminum stakes that I use for the stove stand, an empty water bottle for fuel, and an elastic band to hold it all together. It slides into one of my side pockets on my pack, and counterbalances against my water bottle on the other side. Simple to make, efficient once you get it tuned in, and made with common materials. Cant really get any better than that!