There are small electrical devices called Peltier Junctions which are solid-state heat pumps. A 12 volt one cost me about $35 a couple of years ago, but I never did a whole lot with it. You can build a cooler out of one of these that will probably freeze ice if it is well-insulated. Likewise you could probably build a hot plate to boil water on. Of course you would need electricity but the benefit here is size. The 12v model is only a little over an inch square, and an array of about 4 could probably be the basis for a small refrigerator. They are flat (about 1/8'' thick) with ceramic faces and connection wires. The polarity of the voltage determines the direction of the heat flow in the device. You have to use heat sinks so it won't burn up for most uses, I think.
If someone has a reliable power source, someone might be able to heat / cook without a fire. Because of the nature of the device, it might be possible to make a dual refrigerator / oven - a small, dual-compartment metal box - where Peltiers are mounted in the middle and thus one compartment would get cold while the other compartment would get hot. Only drawback is the power supply must be continuous, but perhaps not especially powerful. (12v, 1/2 amp maybe)
c o l d
-- [-] 12v
h o t
Or maybe hot / cold, doesn't really matter =)
Offered by Joe.