The "oven" pot is the largest, heaviest part of the baking system, and has the most restrictions on its form--but that's not to say there aren't a LOT of options.

The most well-known pot of this type, though most people have never used one in this way, is the dutch oven. While these days they're mostly used as heavyweight stew-pots or for baking cobblers with direct heat, they were originally popularized as actual ovens--chambers in which one would place a smaller pan for baking. If you're interested in the historical usage of Dutch ovens, here's a man in a funny hat who would love to tell you more.

For car campers or the inordinately strong-backed, they still excel at this function. Your grandparents' cast iron dutch oven will do a great job baking on a propane stove or campfire. Of course, their size and weight mean that most of us would rather not carry them further than from the car to the fire ring. Horace Kephart, in his 1906 book Camping and Woodcraft, says, "A Dutch oven of cast-iron is very serviceable on any trip that permits carrying so heavy a utensil. Why are there none made of cast aluminum?"

Well, in the intervening 110 years, one or two companies have taken notice and aluminum dutch ovens are now indeed available at around 1/3 the weight of their cast-iron cousins, and have the added benefit of conducting heat even better than cast iron. Even these, though, are not ideal for backpacking.

For those who carry their kitchens on their backs, a standard thin-walled backpacking pot has the potential to bake almost as well as as a heavy dutch oven with just a few modifications and things to avoid.

Material

Almost any material used for backpacking pots is suitable for an oven pot. One must be careful with aluminum, since without the immediate contact of food or water to pull heat away from the pot, too much heat too fast can cause the aluminum to melt--but at the low stove power required for baking, this can be easily avoided. The best aluminum pots are hard-anodized to appear dark gray in color rather than bright and shiny.

Stainless steel is a very good option. Though a bit on the heavy side, it's durable and won't melt.

Titanium is even more heat-tolerant than steel, and a fair bit lighter.

DO NOT USE A NON-STICK POT FOR YOUR OVEN. The coating, whether it's Teflon or some gimmicky "ceramic" coating, has the strong potential to overheat without the direct contact of food or water to pull heat away. If the coating overheats, it will not only ruin the pan but also release toxic fumes.

Whatever material your pot is, it needs to have a reasonably snug-fitting metal lid. The pot itself and the air inside of it will likely get hot enough to melt a plastic lid, so I try to get lids that don't even have a plastic handles.