I feel this topic needs a rousing and add a recipe of my own. When I was interning (no pay, lots of work and living in a dorm all summer without a real kitchen) I would stock up on cans of black beans (or any bean), corn, and jars of salsa. Every morning I would dump a can of corn, beans, and a couple tablespoons of salsa into a tupperware container. If I had time/the facilities I would microwave it, but it can also been eaten as a cold salad.
It's an easy meal that ends up costing about $1.75. Which on no money utterly rocks.
Now that I am actually working for money, I still find I go back to this. Now I tend to add chopped onions, basil, cheese, green olives, and anything else I have handy. Also, it is rare that I don't have a microwave so I almost always microwave it.