A Jerry can covered with a cloth in a half-filled sink will keep cool.
A Coolbox will stay cold longer if it fits into an insulated locker under a foam mattress. A good lid seal is essential – and it should grip a five-pound note.
Frozen food takes about three days to thaw in a well-insulated box

Or you can keep cheese in jars of olive oil, and cooked meals can be preserved by bottling them in a pressure cookers