My kids get hot lunch AND they want to bring like 4 snacks. It really upsets me as well. I cringe at what they eat. When they get home they tend to snack more on the fruits/veggies if prepared so when I am feeling very guilty of all the processed garbage I will have cut up cucumbers, peppers, oranges for them when they get home. They won't eat the fruits and veggies at school.
My son is 12 and on a health kick and will only take fruits and veggies. I have to BEG him to eat chips and cookies so I guess you can't win.