If your kids buy school lunch, go over the menu with them in the morning and discuss what food options they have. One rule in our house is that they must have a fruit or vege with every meal. So where I may give on the chicken nuggets, we have agreed that they will also eat the oranges.
If your kids bring a sack lunch you have more control over what they eat. When I pack lunches for my boys I usually either give them lean ham or turkey deli meat rolled up, a cheese stick, grapes, 100% juice box, cheddar bunnies or pretzels.
Another item my kids love for lunch is "home-made" lunchables. I buy a Hormel All Natural Ham and cut it up in cubes, add cheese cubes and healthy whole grain crackers and you have the healthy version of a lunchable. Then you can add grapes and 100% juice box or low-fat milk and they have a good healthy lunch to get them through the rest of the day.
picture from keetsa.com