I have made casseroles using a white sauce (easy to do, look in any basic cookbook) and leftover vegetables (or frozen or fresh) and one or two cans of beans. The vegetables are particularly good if you cook them first in broth. Use any casserole recipe you find for the general proportions and just substitute with whatever you have on hand. Potatoes or yams are particularly good for extending the recipe. I also use basically the same technique but in a pie shell for a pot-pie. You can also use a biscuit topping. If you make your own white sauce (instead of using a canned soup), you use low-fat milk or soy milk or whatever your preference. You can also add cheese to the sauce if you wanted to. After you have some experience with making things like that, it is fun to experiment or just use up ALL the leftovers. Nothing I make ever tastes the same twice in a row!