Ground beef cooked up with taco seasoning (or your own combination of spices) is a great, low-cost ingredient for a meal. Just put it in a spill-proof container with some lettuce, shredded cheese, and tomatoes, and include a small bag of tortilla chips on the side. (You don't want to combine the chips with the meat until it's time to eat, otherwise they'll get soggy.) Canned corn and black beans are also great additions to this salad -- they fit with the Tex-Mex theme, but the beans add protein and the corn provides essential vitamins and nutrients. Top with salsa or sour cream for added flavor.