This tip is courtesy of my mom. For years, whenever she cooks chicken breasts in the crockpot she throws in a couple extra to put in the freezer for use in a casserole on another day. I have issues with touching meat, raw or cooked, so cooking more at once works for me (and my issues).
1. Take a bag of chicken (above).
2. Dump it into a crockpot (below). Cook on high for about six hours or low for about 10 hours. I often turn it on before I go to bed and let it cook all night.
3. Take the chicken out of the crockpot and let it cool. Divide it into ziploc bags and freeze. When you need cooked chicken for a casserole, just defrost a bag of chicken and throw it into the bowl!
You can also do this with hamburger. HERE