My son was the same way and I found the best option was pizza...it kept him full and had a few of the food groups. He would eat it cold. I would get a pizza on Sunday night and then pack it for a few days in his lunch. By Thurs I would either need another pizza or find him something else. He now likes spaghetti o's in a thermos. They seem to stay warm enough.

Tortilla roll-ups? We even do PBJ on a tortilla, but lunch meat, veggies, almost any sandwich filling works. Might be too sandwich-like for some kids. We have done things with dips, too. Tortillas (again) with hummus or even cold or Thermos of refried beans, crackers with peanut butter dip with a tinsy bit of honey to call it honey dip. I have also noticed in the stores lots of bento style boxes. In these you can put almost anything chopped up or sliced in each little compartment. Seems like that would be fun, though we have not tried those yet. Hope it helps :0)

My son will only eat chicken nuggets, so I know the fear about school lunch! We actually started out in primary school sending his nuggets and crackers, but also had his aide get him to at least try a school lunch. Some of them he actually liked and others he would just throw the tray! If he didn't eat the school lunch, his aide would make his chicken nuggets. They had a microwave in the special ed teacher's office and we got permission for the aide to use it.

If this is something that your son needs then I would most definitly 1st call to see if they will accomadate this need without having to add it to his IEP but if you have a school that wants to be difficult then I would definitly write a letter of request for an addendum meeting to add it to your IEP! I would explain it to the school exactly like you did it here! :)
This may be something you could discuss with a nutrionist to make sure he is getting the adequate nutrition while at school???

Anything that is a finger food that does not need to be reheated. Just as long as they eat.