My family follows the Primal Blueprint dietary recommendations, which is no grains, limited sugars (getting sugars from natural sources like fruits and honey, etc.), basically a very whole foods based diet. My kids always have filling and healthy lunches. I use bento boxes and silicone cups (most are like small or mini muffin size) so that I can keep things separated.
We do meat and cheese lettuce wraps. I send leftover dinners (chicken, steak, hamburger patties, meatballs) that don't need to be reheated; most things taste fine at a room temp, especially to children. I've sent no-bean chili in a thermos as well as homemade chicken soup with no noodles. I've sent chicken sausages with a side of baby spinach with very small miniature dressing of olive oil and balsamic vinegar. I also include one half to one whole piece of fruit and sometimes include a small amount of honey-sweetened yogurt with sprinkled cinnamon that my kids love. My kids are also seafood fans, so I've sent tuna salad with celery or cucumbers to use to eat the salad with. They've also taken just plain tuna as well. Another of their favorites is smoked salmon (home made). Hard-boiled eggs are another great idea, and I recently got some cute shapers for these (to make them into fish, heart, star, etc.), but I haven't done them yet. Feel free to ask if you need more ideas. I'm sure I can come up with more.