Lentils with old vegetables from the back of the crisper drawer make a delicious, filling, and inexpensive meal.
Pre-cooked lentils keep in the refrigerator for months (try these: http://www.melissas.com/Steamed-Lentils-p/28.htm). When the lentils are cooked, the dish can be prepared in a few minutes. Dried lentils are very inexpensive (feeding 8-10 people for $1.50) and have a long shelf life but need to be cooked for 30 - 45 minutes.