My son is now in 3rd grade but I'm still always looking for ideas!
Home made Lunchables are great - keep it simple for preschoolers tho- make them PB& cracker sandwiches instead of bread sandwiches.
I've done things like spread cream cheese and thin lunchmeat on tortilla, roll up and slice into circles. But that goes into an insulated lunch box with a small bottle of water that has had about 1/3 of it frozen in the fridge to act like an ice pack.
Veggies are best eaten when there is a small dipping container like ranch. Or salt for cucumber slices.
I do grilled cheese tortillas (quesadillas) and they are great. mm I think I'll go make me one for lunch right now! ;-)