I use a "cool bag" (insulated shopping bag keeps food cold or hot) from the supermarket with an ice pack thrown in for good measure. I also pack my water bottle on top for easy access. In 40C + weather you look forward to stopping in the shade for a drink. Frozen food won't stay totally frozen but good enough to get it home - way better than the boot of a car! These cool bags are great - use in the winter too as pretty much waterproof but the cheaper supermarket ones don't stand up to daily abuse.