I think you'll find if you do any research at all that there is no limit to how much you can spend outfitting your child's lunch kit. I've done a fair bit of research and a bit of trial and error to arrive at this list of preferred items.
Food containers
You are going to need lots. As you find how readily containers get lost or misplaced you may adjust how much you invest in them. I've settled on Ziploc containers for sandwiches and snacks. They get the job done and since they can easily be found at my grocery store, are easily replaced. The brand really isn't important so much as the sizes you'll need. For each child, I'd start the school year off with 3 or 4 small square containers for sandwiches (709 ml); 3 or 4 small rectangle containers for homemade granola bars or squares, combo vegetable action, wraps, peeled orange pieces, etc. (236 ml). Finally, you'll need at least 6 extra small containers for snacks in general like gold fish, carrot sticks, etc. (118 ml).
Squooshi Reusable Food Pouches
For applesauce or yoghurt or whatever. I have one that my son's grade 1 teacher gave him as a prize, still going strong. The inventor of this should get a Nobel prize.
Swissmar Vegetable Peeler
The greatest vegetable peeler on the planet — but I use it for slicing cheese for sandwiches.
A Zester/Cheese Grater
For parmesan cheese on pasta and more.
Thermoses
I use both the Thermos Funtainer Food Jar 10 oz (perfect portion size for grades K–3) and the Thermos Stainless King 16 oz (perfect portion size for grades 4–6). Sometimes my son gets the big one as well for leftovers, but the small one works great for pasta and soup. Remember to preheat with some hot tap water or boiling water for at least 10 minutes before emptying and adding your kid's lunch. This is a necessary step to ensure the food is still hot by lunchtime.
Nalgene Insulated Bottle Carrier with zippered top
This might be overkill but the thermoses fit perfectly inside of it and it gives me peace of mind that even though this is going in the same lunch box as the ice pack, the food in the thermos will stay hot, and the food in the lunch box will stay cold. Also, there is enough room to fit one of the extra small square containers to add crackers for soup or tortilla chips for chili. Otherwise, the little munchkins will almost assuredly eat the soup crackers early and then have a lunchtime of regret.
Thin ice packs for lunchboxes
You just need to keep it cold for a few hours and I think I bought a 4-pack of the cheapest version I could find 6 years ago.