I have a large container in my fridge's freezer. I toss all leftovers in that.....eventually I add cans of Italian stewed tomatoes and make a " 'fridgerater stew".
My GF has a 2nd container in her freezer -- she adds all juices from canned fruit, etc. Eventually she adds pectin to it and makes jelly. I did it once, but I'm not much of a canner.
I will take leftover chicken or steak chopped up small and put on a tortilla, add any leftover vegetables and some cheese and either heat in a pan or toaster oven.