I recently remembered a nifty trick from my childhood in Australia. Take a small fruit drink in a box, the type you stick a little straw into (we called them a fruit box), and pop it into the freezer. Easy peasy! Once frozen you can either rip the top off (you’ll need scissors-they’re tough little suckers) and eat as ice lolly or stick in lunch box. Keeps things cool till lunch and will melt in time for you to have a cool drink as well.