With pasta I take all the leftovers and put them into freezer containers and stick them in the freezer and then I use the whenever I need a bit of pasta, as in chicken noodle soup, or as you say casseroles.
For soup, it's funny most people say they use their leftovers to make soup, not what to do with it once you've got it. ;) But I did find one suggestion, to freeze it into serving sided containers, and then it's lunch, but later, instead of tomorrow. I think I'll try it out and see how it goes, as I don't by canned soups, the sodium is just to high. Salt to have flavor doesn't really work for me.