If you're stuck for ideas, here's a few.
quick chicken supreme work well with other poultry such as turkey, if you bought a small crown, guinea fowl or duck. And so will my cheat's chicken cacciatore - just make the sauce without the uncooked chicken, then add the cooked meat 10 minutes before the end, so it's thoroughly reheated.
chicken and vegetable pie or chicken risotto.
lamb in date and lemon sauce says uncooked lamb, but cooked will be fine - you'll be basically reheating it in the sauce in the oven. You can do the same with my fruity goat tagine - it doesn't have to be goat meat: leftover lamb or chicken will both be fine. A couple of slices of cooked lamb can also substitute for fresh chops in my lamb chops baked in the oven.
game soup is ideal for leftover partridge, pheasant or other roast birds. My quick winter minestrone is very adaptable - the tomatoes, greens and pasta are the backbone, then just throw whatever else you have to hand in it.
winter root veg casserole is tasty and also simple and light after the richer food of Christmas Day.
Don't forget, quite a few of these can also be frozen once made - handy for those days when you don't feel like cooking but can pull something home-cooked from the freezer!