Steak. You can pretty much figure out how to cook it the way you like it, with whatever you have to cook it with, and just do it over and over again.

Also, doesn't have to be expensive. I'm always able to find steaks in the supermarket bargain bin, as long as I'm not picky. Lots of thin-cut in there, which is also super-fast easy cook. You could cook them on a foreman grill if you had to.