Primitive or emergency cooking is accomplished usually with improvised culinary tools or perhaps with none at all. Many foods can be placed right on ash-covered coals to roast. Tubers and roots when placed on coals will turn black on the outside but the skin can be peeled off and the remaining portion tastes great, often with intensified flavors.
Larger potatoes take time to cook so an alternative method is used if you don’t have an oven. By encasing a potato or “spud” with mud you can protect it from being burned and more evenly distribute the heat. If you like eating the potato peel, you can first cover the potato with leaves or even wet newspaper, otherwise, the skin is a barrier to the starch inside. When covering your spud, clay is the preferred material as it adheres together well whereas regular soil may not hold together and cracks more easily.
The last time I had baked spuds my friend made some with straight clay and with others he included grass in the clay mix. The ones with grass held together better. We placed them on the campfire coals and also built a fire on top of them. After an hour they were ready to eat.
We had one left over that night and the next morning we opened it to find that it was still warm and very edible. If you try this on your next camping trip you might consider “planned-overs” for breakfast the next morning.