As a ‘natural’ input, IMO (Indigenous Microorganisms) can be made on site very inexpensively, or in the case of EM (Effective Microorganisms), purchased also very inexpensively. And a little, goes a long way.
Charcoal has been used to make fires for thousands of years of human history. High temperatures made it useful in the Iron Age. High temperature & lack of smoke when burning, and higher energy density compared to wood, make it very attractive as a fuel for cooking.