We have the same issue and our son is in daycare 5 days a week unfortunately. Here is an idea of what we pack, but we have a very picky son. I look forward to reading the other suggestions you get for some new ideas...
We send a cold pack in our son's lunch bag and warm items get sent warmed and in a thermos or insulated bowl... I don't really like sending the warm items, but he was getting tired of sandwiches so we had to try something...
PBJ (obviously)
Bologna (or other lunchmeat) sandwiches
Lunchables
Spaghetti
Spaghettio's
Soups
Chicken Nuggets
Rice or Mashed Potatoes
Not much of a selection, but what can you do... Then of course he gets other items like fruit, crackers or bread with butter, sometimes chips but not often, yogurt, and a treat like a small cookie, pudding, or fruit snacks, etc.
I like to send him with V-8 Fusion juices often so I know he's getting his veggies also. Another thing I do for drinks is Pedia Sure. He loves them and I know that even if he just picks at his lunch, he's still getting the nutrients he needs...
Hope that helps a little. Good luck! Can't wait to see what other ideas you get.