Mostly it's a vegetable (tomato sauce), starch (noodles), and meat. Dairy is not required but I've seen plenty of hot dishes containing celery, potato chips, apples, whatever.

Pretty much. My grandmother made something called tater tot casserole: a mix of ground beef, frozen tater tots, canned beans, and mystery spices that went stale sometime in the last ice age. This was covered with about half a kilo of cheese and baked until a point she couldn't quite articulate but "just knew".