Not only does my son attend a nut-free school, but I work there as well, and have seen many a nut-free lunch.
My son used to bring soybutter and jelly or cream cheese and jelly every day, or sometime a super-delux as he calls it which is soybutter AND cream cheese and jelly. Sometimes I would put frozen berries in the sandwich with the other ingredients and by lunch time they were thawed out in there. And another big hit was to make one of these sandwiches on a waffle. We called it the waffle-wich.
Now that he's a little older he doesn't like to bring that every day, so sometimes he brings sliced turkey or ham rolled up, or hard boiled eggs (his new fave) or even pancakes.
Besides hot dogs, mac & cheese, and nuggets, I've seen pizza, cut up veggie burgers, regular pasta (with tomato sauce), rice and stuff (rice & chicken, rice & beans, rice & veg) noodles, dumplings, crackers and cheese and pepperoni, grilled cheese sandwiches, spaghetti-o's (and all their Chef Boy-r-dee cousins), and a variety of soups. Most kids in our center own a thermos for bringing anything "warm" as we don't heat lunches for kids.
I hope all that helps. Good luck! (ps, most kids adjust quite nicely to the nut free lunch thing. I've only ever known one kid in 4 years of nut free-ness who had a hard time because all he would eat was PB&J. He eventually caved and settled for soy butter, but one in hundreds is pretty good.)