What i had try this summer was I get a sponge ( a pack of 3 can cost $.99) I place it in a container full of water then place the sponge in a sandwich bag and freeze it and then place it in a lunch bag or insulated bad!
I like the soft sided lunch bags. My daughter has one that looks like a purse. My son has a blue one that's just a small rectangle shape
When my oldest went to school, I used to include notes in his lunch box. "I'm proud of you" "Enjoy your lunch!", "I love you", etc. These are not only fun but helpful for the child who may be a bit homesick while at schoool.