if you aren’t using one of those , i would think that american cheese singles like Kraft onces do not need refridgeration. cheese and bread sandwiches with an apple . peanut butter /jelly.

you can take a thermos and put chilli in it or soup and it will stay warm. you can send crackers or a nice crusty roll along and some fruit. a thermos can also have boiled water and a hot dog. bun on side. chips. fruit.

cheese crackers or peanut butter cracker packages/ granola bar and a fruits , grapes / apple, plum, banana. you know your child and what they will eat . basically they just need as good as nutrition as possible balanced with what they will actually eat.