My next tip is foods. Pack items that you know your kids will eat. Try things at dinner time or on the weekend and pack them things they like, will eat, and can fill them up. The last thing you want is your child to be not eating at school. I really love the Bentgo boxes that help create small serving sizes. It makes meal planning so much easier because you see how much of each item. 

Personally I like to throw in a large portion of the "meal", think pasta salad, sandwich, casserole, etc. I do at least one fruit, a snack item, some veggies if they aren't in the meal, and the little circle in the middle I'll add a treat.