Have you heard stories of the italian pot of sauce? It seems to be like a pot of soup, where you put all the leftovers! Mine is fairly simple, I usually just use tomato puree, spices, garlic and onion and meat if I have it.
But I have heard tell of adding leftover meat, green, re, yellow peppers, and any other vegetabel that strikes your fancy.
Olives would be good, I suppose, but would you throw your leftover potatoes in?