Young inventor Emily Cummins came up with this ingenious low-tech solar fridge which works through water evaporation when she was just 21. Two years later she now regularly travels to Africa to give away the design to any community that can benefit. It’s cheap to make, effective (cooling down to 6 degrees in the middle of a hot day) and portable. Just awesome. More on her site.
The outer shell of the device can be made with whatever materials may be handy (including wood or plastic), while the inner drum is crafted from metal. Soaking the layer between both cylinders with water (dirty works just as well as clean, since the inner unit is sealed) begins and evaporative cooling process that keeps the contents cold as long as it remains wet. Beyond making for a neat piece of camping gear, it can help preserve food for people in places without electricity all over the globe.