Bamboo Farm

Same observer-piston trick as sugarcane, but bamboo skips the water requirement entirely. It grows on plain dirt, sand, even gravel, purely off light and time, and it grows faster than sugarcane does per stalk. If your goal is fuel rather than paper, this is the better plant.

Plant it, put an observer facing the stalk one block above the base, piston next to that. Bamboo shoots up in uneven jumps, so most designs aim the harvest low, around one to two blocks up, before it can reach the taller growth stages that are slower to knock over.

No water source means you can stack these vertically much tighter than sugarcane. Multiple floors of bamboo columns directly on top of each other, each with its own hopper line, is a normal way to cram a large farm into almost no footprint. That's the real advantage over sugarcane if fuel is the point.

By count, a bamboo stalk smelts for the same amount as a piece of coal-tier fuel, but bamboo grows so densely and so fast that a modest farm will out-produce nearly every other renewable fuel source you could build in the same space. It's also the only food pandas eat, so a small patch next to a pen covers breeding for free.

If you've already got a sugarcane farm running, don't bother building a separate structure. Same observer, same piston, same hopper setup. Just run a parallel row of bamboo on dirt beside it.