Are you making dinner tonight? If you are, why not make a double batch. Instead of 4 chicken breasts, make 8. Instead of cooking up one batch of meatballs, make double. Instead of one lasagna, assemble two. Wrap the extra portion well (freezer bags, plastic wrap covered with foil, etc) and place in your freezer. Make sure you LABEL the package with what it is and the date you put it in there. And if there are special instructions for reheating, put those somewhere you'll find them easily. Then, next week when you've just had a crazy day, pull out that frozen meal, reheat it (or cook your pre-assembled item) and serve your family something hot and homemade.
If you are feeling especially ambitious and want to really make make-ahead meals a staple in your family check out Once A Week Cooking or request the book Don't Panic, Dinner's In The Freezer by Susie Martinez, Bonnie Garcia & Vanda Howell at your local library or bookstore.