what ingredients/types of food still taste good after several hours?

I think Hainan Chicken with the rice would make a good room temperature lunch.

I regularly devour Momofuku's soy sauce eggs in similar situations. They'd pair well with the recommended bentos. :)

https://food52.com/recipes/35930-momofuku-s-soy-sauce-eggs

and somehow the link did not paste...

https://food52.com/recipes/14244-quinoa-and-kale-crustless-quiche

This wonderful recipe (crustless quinoa quiche) could be used by NASA to replace any meal of the day in space. I have certainly personally eaten it for breakfast, lunch or dinner and it holds well for a few days. Good reheated or at room temp. I like it with broccoli rabe but you can change up the greens to person taste or what is on hand.

Orzo, farro & lentil salads hold up well.

Derek - I forgot to mention. My daughter makes what's really a bento box with things in the house she really likes. Right now we have homemade refrigerator pickles. She makes salads from our garden as I mentioned. She adds hummus, yogurt, nuts, seeds. She's a swimmer so she needs snacks throughout the day. Like you she's a cook and we have spoiled her with good fresh healthy food at home so she cooks that way so she's not eating any differently at school. When winter comes things may change. But she also loves leftover tandoori chicken

Many choices IMO. Frozen edamame pods (which will thaw by lunchtime) and combine equal parts soy sauce and fresh lemon juice for dipping (pack in a small plastic container, Rubbermaid makes a perfect size). If you are concerned about coldness, the night before place a bottle of water in the freezer and add this to your carrying container. It will not only keep things cold, but you will have your beverage as well.
Mason Jar meals are great as everything goes into the jar! Using a quart jar add your oil and vinegar dressing of choice, then sliced carrots, radishes, celery and end with salad greens at the top. You can get as creative as you'd like! When time to eat, shake the bottle and either mix together in the jar or transfer to a plate. Again, a frozen water bottle would be great to keep this cold, but it doesn't need to be. Pack a couple of cheese sticks and a piece of Italian bread that you enjoy.

I enjoy cold spaghetti that I make the night before. Real easy. Cooked spaghetti, tossed with lemon juice, a little butter or olive oil, capers, black olives. A Mason jar would work for packing it up. Pack a mozzarella snack stick and slice it up over the spaghetti before eating. A nice roll or bread, veggie sticks and a brownie/cookies would make a great meal!
Rice cakes are magical! All kinds of flavors, all kinds of toppings from peanut butter, Nutella, cream cheese, compound butters and topped with avocados, sliced veggies, fruit, nuts, even chocolate chips, you make the combination and taste profile that you like. I would pack the spreads in small containers and assemble with the topping right before eating. Rice cakes get soggy if made in advance.
Tortilla roll ups are great, again, you add whatever you want, roll them up and wrap tight with plastic wrap.
Frozen Grapes are delicious and keep other food cold. For a snack or with your lunch.
Pickles, olive, pepperocini, all good and no refrigeration necessary.
Marinated vegetables cauliflower, asparagus, artichoke hearts, carrots, onions, peppers.
I make my self 'snack packs', even for home. Carrot sticks, celery sticks, radish slices, broccoli florets, fresh pea pods (when in season), sliced red/orange/yellow/green peppers and keep them in a small zip lock bag in the fridge.
Many companies make snack size cheese slices individually wrapped. I'd recommend packing the frozen water bottle if you using these, but they are wonderful!
I could go on and on but there are lots and lots of options!
Enjoy!
BB

Hi Derek- while produce is still good my daughter has been packing a simple salad of tomatoes, basil, mozzarella pearls & balsamic vinegar

I'd probably move away from typical dinner options unless you have use of a microwave (which I know you don't).

For myself, soup in a thermos with some bread and cheese on the side is awesome. A Bento box of deviled eggs, sliced meats, rice paper rolls and other such munchies are fun.

Here's a list of articles that Food52 had going about lunch a while back.

https://food52.com/blog/search?q=Lunch

Also, here's an awesome salad that I'm obsessed with during the heat wave. You can keep the marinated vegetables and meat separate from the salad greens by placing the dry salad greens (I've been using romaine which holds up well with the marinated mixture) on top of the veggies and meat in the container.

http://cooking.nytimes.com/recipes/1015005-escabeche-salad?action=click&module=Recipebox®ion=cooked&pgType=recipebox&rank=1