Blimey, I'm much more downmarket than the people who have posted so far.

Here's the kind of thing I do:
Fry up an onion or two, optional garlic, dump in 2 or 3 cans of tuna (drained), add a can of chopped tomatoes and a bit of chilli powder. Serve with pasta and grated cheese. Or do the exact same recipe with cans of sardines/pilchards in tomato sauce instead of using tuna.
Fry up some mushrooms, onions and cheapo frying steak. Add a carton or two (depending on how much you're making) of passatta and 2-3 beef stock cubes, optional herbs. Serve with pasta, grated cheese too if you want it.
Fry up some onion, mushrooms, diced chicken breast and bacon. Bung on some carbonara sauce or make it. Season. Serve with pasta.
Fry up some onion, mushrooms and chicken livers. Add soured cream. Season. Serve with pasta.
Fry up some diced chicken and onion, add canned ratatouille. Season. Serve with pasta and grate some cheese on too.
Fry up some cabbage, onion and diced pork. Add soured cream and cottage cheese. Serve with pasta. Bit bland that one.
Fry up some onion, thinly sliced carrot and diced chicken. Add any or all of aubergine, courgette, mushrooms. Chuck in a tin of tomato soup. Grate some cheese in there. Serve with pasta.
I often play around with the ingredients a bit, changing things here and there, adding a little this or a little that.