Looks like my suggestions will be similiar to some of the others but I will send them anyway. My son ate bread but only liked ham, turkey, or jelly (with NOTHING else) on it so I understand you dilema.
You can make your own lunchables: cut lunch meat and cheeses(whatever kinds your son will eat, cut a bit thicker than normal) into rectangular shapes about the size of the crackers you choose. If the daycare provider will put the "sandwich" together" great, if not your son can eat the ingredients separately. You can also use tuna, chicken, or egg salad instead of the lunch meat.
Will your daycare provider cook something you send? You can send fish sticks or chicken nuggets and instand mashed potatoes or rice. You could send the fixings for a grilled cheese and send soups to go with either of those.
Dinty Moore has some "all in one" meals like chicken and dumplings, turkey or beef stews, chicken and rice, turkey and dressing, chicken or beef with potatoes, etc. that take 90 seconds in the microwave.
Additional items to send as sides would be fruit cups (any variety), carrot sticks, and/or applesauce. There are now also frozen kids dinners (like nuggets or fishsticks with mac & cheese, a vegetable, and a snack).
Good luck!