Leftovers of things like spaghetti sauce, taco meat and chili need not be tossed just because it isn't enough for my husband's lunch the next day. I just have a small labeled tupperware (or reused spreadable butter) container in the freezer and place the leftover in it immediately after dinner. No more confusing random containers in the refrigerator that have to be thrown out because noone remembered to eat them! After the container is full, I just use the frozen spaghetti sauce or taco meat the next time we want to eat it.
When we have chili on our hotdogs we never eat it all, so there's a chili container in the freezer. Another thing I noticed is that a recipe of Cranberry Catalina chicken (Boneless skinless chicken breasts with whole berry cranberry sauce, bottled Catalina dressing and Lipton dry French Onion soup) is enough for 8 chicken breasts, and I only need 4 (in truth 3, but my husband usually eats the other one for next day's lunch). Half of the can of whole berry cranberry sauce goes into a labeled contained in the freezer for use another day. Easy and both frugal and environmentally conscious. :)