When factors like emissions, renewability, and heat / energy efficiency are all taken into account, what would be the very best fuel source(s) to use for camping cooking, with sustainability and environmental impact in mind?
If in the case of alcohols (such ethanol), you might assume I produce my own - as in grow my own sugar cane (sustainably), harvest the sugar, or, use an alternative biomass like my own wood waste, produce my own brewer's yeast and brew my own (efficient-burning) ethanol myself. Or if wood, I would gather fallen wood from the natural environment around me. Even in the case of coal, (though I don't assume it the most sustainable fuel), there are actually natural open-air coal seams in places I frequent that I could technically gather and burn, as opposed to buying it.
I assume though that some fuels are out of the scope of self-production / sustainable gathering such as highly-processed petroleum-based fuels (e.g. industrial kerosene).
But for each case I would like to compare their very best (sustainably DIY) possibilities in their own right (where growing or sustainably gathering obviously is much more sustainable than purchasing ready-made materials), within practical reason such as the examples above.
So what would be the best one(s)?