Then some bedding material. It releases heat through out the night. Many would-be survivors try starting the tinderball from the top or side. The flames need to spread across as much of the surface of the tinderball as possible. Starting it low from the underside all the way around is the best.
Rocks taken from wet locations can be full of moisture.
When the rock is heat in a fire the moisture tries to escape rapidly and can cause the rock to explode. This is a common place event don t take chances. Rock boiling is used when a fireproof container is not available. Heated rocks are placed into what ever kind of container to super heat the contents and bring it to a boil. Construct a lean-to of some make and model and build the fire under it.