Sharing the same qualities that make the cast iron pans attractive to apocalyptic cooking an preparedness, namely their ruggedness, good thermal transfer and thermal retention properties that is part and parcel with cast iron products. I have quite the collection of cast-iron pots, which get more use in regular rotation in our regular cooking, beside we like to cook a lot of long and slow.
The down-sides are the same too, its heavy, a touch brittle and can rust if not maintained. There is also quite a variety of sizes and styles of pots as well, but the key points to look for are the combinations of lips, handles and hangers. Lids are of course highly desirable, and also have some variety. I have a range of pots, from the massive 20L, through to the tiny 150mL ones.
As I've been collecting these for some years, I've come by them in several different ways. The biggest pop cam by way of Omega and her own reenacting past, the lipped large pot can from a disposal store, where as the two mid sized pots came from second-hand shops, and didn't come with lids. The littlest ones came from a cookware shop, for fancy sizzle cooking, but cast-iron is cast-iron!
I'm most pleased with my legged Dutch Oven, with its tripod feet allowing it to be placed over coals and cook in ashes without needing a standalone tripod, and settling on uneven ground without spilling. It also comes with a lipped lid, with a solid handle. The lipped lid lets you stack coals on top allowing you to cook evenly on all sides.
For those screaming at me for the rusty look of my pots, giving them a good clean and re-season is usually as easy as a bit of a scrub, heating it till good and hot to burn off any stuck food and water, then re-oiling. I use spray-on vegetable oil from a can to get a even thin layer, and it works really well, as you can see here, following camping for 6 days over Easter.
I bake cakes and bread in mine (for cakes I tend to nest one pot in the other as seen here, with spacers between the pots to distribute the heat a bit). Delicious and magical for all the ramen-noodle and sachet cooking crowd.
I also cook directly in them, both stews, chili and roasts. They also serve to keep hot food hot, as different dishes are prepared, and as well-sealing serving containers, keeping both germs, bugs and critters out, especially if closed when its sizzling.
The other thing I look for in cast-iron pots is nesting for storage and transport. Cast-iron is be necessity, heavy, and sometimes difficult to pack, store and transport, so having all that in one place can be an advantage (or not, depending). I like mine to nest.
I take them away with me on almost every camping trip, which I'm not hiking all my own gear, which is when I'd use my lightweight gear, like the Optimus: Terra-solo cook or the Power Practical: Power-Pot. For old-timey camping or homesteading, you really can't go past the rugged and robust charm of cast-iron though. It takes a lot of abuse, cooks delicious food and lasts a long, long time.