You could make it more of a *snack meal*, eliminating a sandwich. Pack 3 or 4 smaller things--string cheese, fruit, fresh veggies, crackers, maybe some cheese to go w/the crackers, peanut butter crackers, hard-boiled egg (peel before packing), pretzels, biscuit or roll, baggie of dry cereal, etc. I'd try to keep it to more healthy choices and avoid the processed/packaged stuff.
Will they eat cold/lukewarm pizza? You could bake a frozen pizza an hour or so in advance and pack a slice or 2 for each of them along along w/some other things off the list.
I think doing a *snack meal* would tide them over until the practices are over. If they're hungry again by the time they get home, you could give them a little something more substantial then.