As I live in Namibia, where hot spells last longer than cold spells, during the times before electricity was available nationwide, all kinds of devices were created and used for keeping food from spoiling.
a) coal coolers: Often big enough to walk into. The inner wall is continuous. In the outer wall the bricks are put on top of each other leaving a gap between. Otften a chicken-wire mesh is also put in. Thencleaned charcoal is packed between the two walls. The charcoal is watered daily. The inside room is cooled through the evaporation from the coals.
b) For travelling and camping. Use two cardboard boxes – from sturdy material – into each other. the gap should be at lest 2 inches all around. Between the boxes pack moistened newspaper – very tight. Keeps cold food atl ow temperature for a couple of days.
c) Canvas Waterbottle. Keeps drinking water cool through the slow evaporation process of water that oozes through the canvas.