I love left overs!
I have young young children so am still able to buy mn magic chickens - if I make a roast chicken I can make up to four meals from it- risotto (make too much for arancini, chicken and stuffing pasties, chicken pie, fried rice, chicken and mushroom lasagne, chicken and salsa enchiladas, chicken soup etc ( not all of these from one chicken but just some things I make with leftover chicken)
Left over mash makes croequettas, fish cakes or ham and cheese cakes
Left over saucy meals- bolognese, chilli, stroganoff are frozen in the portion left to go on jacket spuds - we all pick a topping from the freezer and off we go,
Leftover ham like chicken (and turkey) have endless options- hash cakes with an egg, ham and cheese slices, pizza, quiche, soup, ham and leek pie etc
Leftover roast veg is great in soups, but also in tagines- make up a base sauce with any extra veg you need or chickpeas and add chopped roast veg at the end to heat through
Leftover fish pie makes fish cakes
Leftover roast pork makes great pork and cider mash topped pie.