My own opinion is that most of the weight gain during the holidays is caused by eating up the leftovers.  They're there... you don't want to waste them... they're calling your name.

Be smart.  Some things, like Cranberry Relish, for instance. don't freeze well and will accompany meals for several days.   Pies, personally, I just eat and get it over with.  But stuffing, turkey, ham, goose or whatever you have served as the main dish, plus all those casseroles, fancy veggie dishes, gravies, sauces and accompaniments can add on the pounds as you snack... and snack... and snack.   (I'm not trying to insult your self-control.  Maybe you have more than I do, but if it's there, I'll eat it!)

First, be safe and put away all perishable foods immediately!   As soon as you have digested your meal, seen your company off or whatever, divide the extra food into meal-sized portions.  Label, including date, and freeze everything you won't use by the next day.  Get it into the freezer where it will be too cold to call your name!

Poultry scraps and bones make GREAT broth.  Even if you don't want soup the next day, process in your pressure cooker, barely covered with water on low fire, for an hour.  Cool somewhat, drain, and refrigerate.  As soon as broth is cooled down (the same day or next morning), skim off fat, label, date and freeze for future tasty soup, fricassee or other dish.

One great use for leftover turkey or goose is to substitute it for chicken in Salad Olivier, a taste treat that will use up leftovers in a hurry.  If you cook potatoes, leftovers can be used, or if you made mashed potatoes, cook extra and leave unmashed to plan ahead, chill promptly and use in the Salad Olivier the next day.