Jill, Congratulations on your wonderful news. I hope everything goes smoothly.
I don't freeze a lot of casseroles, but one thing I always keep in the freezer is boneless, skinless chicken breasts. You can do about a thousand quick things with them, and they don't take too long to thaw. If you have a warehouse-type store nearby where you can get a big bag of the individually frozen breasts or tenders, they're great to have on hand. I also keep a bag of seasoned breading mixed the way my family likes it in the freezer, ready to use, so I can make "oven-fried" chicken breasts or tenders or "nuggets" in a hurry.
Let us know when Baby comes!