I take left over spaghetti, mix the sauce in, throw it in a pan, sprinkle Parmesan over it and top it with Mozzarella. Then I bake it until its hot and the cheese is all gooey. My DD LOVES my spaghetti pie.
Left over Vegetable soup? I strain the vegetables out, add a little more meat, mix some of the broth with instant potatoes and put it all in a pie crust and bake. Voila! Homemade pot pie.
Left over chili, I add macaroni and we have Chili Mac
Mom used to make something she called Refriderator Clean Out. She'd take all the meat (it would only be beef or pork) chop it in with the vegetables, stir in the left over gravy, top with biscuits and bake.