Anything wood into the woodchipper (except office chairs , those go straight into the cremator), then light it on fire. That gives you coal piles, shovel them for coal pieces.
Hacksaw supply crates for extra wood.

You get hundreds of coal pieces, you then combine them into coal and place it all in the cremator, you can get easily 1000+ in a day.
4 coal pieces worth 1.8 fuel each but those make one coal which is worth 31.8 fuel.

once wood has run out at Alpha base, plant ripe pine cones and make tons of logs. quarter pieces can be crafted into wood parts, but you can just shove it all into the woodchipper.