Websites such as Kraft.com and Family Fun has some really great ideas. My girls go to 1/2 day K so they are home for lunch. For the past 2 summers they have spent a week at a day summer camp in which the bring their lunches.
My girls love salads so I was able to make some chef salads for them. (pack dressing separately). Deviled Eggs w/a Cheese Stick was very popular as was a small container of Tuna or Chicken salad served with crackers. They loved making deli wraps which consist of one slice turkey, one slice ham, one slice cheese, spread lightly w/mayo or mustard, add a red or green pepper strip then roll up and secure w/a toothpick or pretzel rod.
My girls loved packing their lunches the night before. I had a list with a week's worth of items (in addition to above, PBJ and Bologna sandwiches were favs). They choose one main dish (examples above), one sweet item (graham cracker, fruit snacks, granola bar, trail mix), one savory item (crackers, goldfish, pretzels), one veggie (salad, carrot sticks, pepper sticks, celery sticks), one fruit (grapes, apple slices, banana slices, pear slices, strawberries, etc)
That seems like a lot, but they would get a very small sampling of each choice. It gave them a lot of variety and encompassed all food groups.