I stumbled across this link the other day which seems rather ingenious and was wondering if anyone has tried such a contraption whilst hiking? If not, do you think it would be effective? I'm tempted to try to make one and then see how it performs in various temperatures.
The one problem I see is that it actually doesn't keep things cold enough. The listed rate is 6°C (42°F). For refridgeration you want no more than 4.4°C (40°F) and ideally want closer to 1°C (34°F).
At 6°C (42°F) it makes that a little more than a growth chamber for many bacterium: Food Safety.