The night before, I freeze about a third of a serving of raw milk in my daughter's Kleen Kanteen, then fill it up in the morning and put in her insulated lunch kit with her food. My dd loves icy milk and loves that it keeps the rest of her food cool. The temp makes a difference in her enjoyment of the food, for sure.
Used to use a thermos for the milk, but found the KK easier to clean, with a bottle brush.
She packs her own lunches now, but I used to stipulate a minimum of 5 items from at least 3 food groups, at least 2 of which had to be fruit/veggie.
I have been canning apples from our trees and pureeing them for applesauce, which is a staple snack for dd's lunches still. I also make a lot of muffins and quickbreads with fruit/pumpkins/zucchini/carrots and they are another staple.
I have a bunch of freezer jam containers
which I now I use for lunches . The lids screw shut which makes them really easy for little hands to open and reseal. I had too many problems with tupperware type lids not being locked on and stuff spilling.
I tried pyrex containers but got complaints they made the lunch kit too heavy. Bought a laptop lunch kit and was disappointed in the poor seals/containers without lids. Too messy. Also, not big enough for an upper elementary school kid's lunch.