Great question and I LOVE the answers! One thing I want to mention is that I encourage all moms to inquire with the teacher if there are any severe food allergies in the classroom. As a mom of 2 children who are life/death allergic to peanuts, lunch time is the scariest part of the day. I actually cringe when the phone rings at lunchtime!
Anyway, freezing small tubs of yogurt is a hit with my kids. Soup in a thermos is my daughter's favorite or make a pasta salad (I love the idea of penne pasta dipping sticks, mentioned in another reply!) with leftovers and their other favorite mix-ins is great.
Another thing that I didn't know until well into the school year, is that I could join my child for lunch! This is a nice treat and you can bring their favorites - even if they're hard to pack in a lunchbox!
AND, know that (at least in LISD) if you fill their cafeteria card with money so that they can buy their lunch, you can also go to the school and make specifications about what YOUR child is allowed to purchase (i.e. restricting ice cream, powerade, other junk that shouldn't be there anyway, at least IMO).
Good luck!
L.
A little about me:
Single mom to 3 awesome kids, 2 boys 8 & 6 and my princess who will be 4 in October!