For campfire baking, I carry a 7" diameter metal mixing bowl. This bowl does many other duties for cooking and washing and hydration, but it's also my oven.
This size obviously would only work for a small 1-person size pizza, but you could do it twice if you had to.
I also have a small cooking grate, but you can make one of those easily, or it could even be a long pair of kebab skewers set between rocks or logs, or whatever you want to rig up as a cooking grid.
And I cut a 6" round plate from aluminum roof flashing material(very thin and light). That's the pizza pan, or cookie sheet, or biscuit sheet, or whatever.
Let the fire go to coals, put the grid over the fire at an appropriate height for a hot bake.
Make your pizza and put it on the round aluminum flat plate on the grid, and put the 7" bowl over it "upside down" as a cover, and that is the "oven". The heat rises around the round pizza pan into the "oven" and is retained there, and the fire heats up the 6" round flat pan under the pizza, for that all-important bottom heat that pizza crust needs.
For cornbread or a big biscuit, I just put the dough in my stainless drinking cup and put that on the grid directly, and cover it with my upside down bowl. Then it all bakes inside the metal cup and no flat plate is required. Sometimes it might stick to the cup, so you might grease the cup or just eat it out of the cup with a spoon, or whatever you want to do.
For cookies, you use the flat round plate.
This is a very useful mini-oven arrangement, and I use it for biscuits and cornbread and other baked items on the trail. Simple, yet effective. The concept is solid. It heats from the bottom, has a heat retention chamber above and around the food, and there is a grate above the heat source. Just like any other oven. When you need a pan for pizza or cookies or something, you add that to the system, and my pan is that 6" flat piece of aluminum roof flashing.
The temperature is set by the height of the system above the coals, and you need to get a "feel" for what that needs to be, after some experience.
And the bowl can be used to make soup/stew, or boil water, or scoop water from a stream for treatment, or for washing up, etc.
A variety of uses, and I use this bowl inside my food pack to hold all my other smaller cooking stuff like my cup and utensils and stuff, and put the flat 6" plate inside on top of everything else to keep it flat, and then stretch a suitable cover over it to hold it all together.
I keep all my cooking and food stuff in one separate food pack/bag to keep odors segregated from my clothes and tent as much as possible. Then I just hang that whole bag up from a tree limb because we don't have bear canister rules around here.