I have a couple things i do. IF you don't mind wasting foil, line your casserole and oil well, put in your casserole then freeze for a few hours. Take it out, wrap the foil around and wrap extra in freezer bag, more foil or whatever depending on how long you plan to freeze. The other option is to just oil the casserole (i like that white corningware a lot) and dump the food in, and freeze a few hours, then take it out and dip in hot water a minute and pry it out with a spatula or something, then wrap in platic wrap or whatever and freeze. then when you take it out just use the same dish you froze it in. I also love to use bread pans the same way.
When I make things like lasagna, shepherds pie, I usually make one for dinner and then freeze a couple smaller ones in bread pans the same way. I like to make different lasagnas since everyone prefers a certain one anyways, so if i make all the stuff for 3 different ones it's not all my time for one meal. Lasagnas BTW are perfect for loaf pans because one noodle fits in the bottom and you can just stack away.
Another favorite thing to do for me is freeze in large muffin tins. These work SO well and make fun dinners. I use the large ones for dh/myself sometimes and regular sized for the kids. You can fill the whole pan up, freeze, then dump out and individually wrap then rebake like mini casseroles