I am in a similar boat for my school aged child who brings lunch to school. I'm out of ideas! They don't have access to a fridge or microwave.
Think "God's packaging". That what I try to teach my kids. We try to have a fruit and veggie at every meal. Also there are great kids cookbooks or try the Family Fun website for some ideas.
We like nitrite free lunch meats, string cheese, any veggies with dip...the dips are peanut butter, ranch dressing, cream cheese, etc. Cottage cheese and yogurt are great and quick. Applesauce, applebutter on toast, bagels, soup and smoothies.
My kids will eat most anything THEY get to help make. I was surprised they love tuna salad, hummus, pesto, V8 and homemade pizzas are always a hit too.
When I make a "big" dinner, like a ham, whole chicken, etc. I make sub sandwiches the next day. The kids love stacking all the meats. We also do "roll ups" - just one piece of meat rolled up into a tube. No bread. Little mess. Great lunch outside on our kids picnic table.
I hope this helps!