Pasta Salad with either shredded chicken, tuna or gourmet'ish grilled veggies.
Cold chicken - as in leftover KFC.
Greek Salad? Greek Pasta Salad?
Sausages? Cook them and keep them warm in foil in a preheated thermos and presautee the onions and bring the saurkraut. Same goes for hotdogs.
Veggie pizza? Its great cold and packs well.
Pudding cups, cupcakes, muffins, fruit salad for dessert? Yoghurt?
The possiblities are endless, so long as you have the means to keep the foods hot/cold and arent trying to feed a picky eater.