For field use a lot of people find the classic 'handy file', a file with a simple punched steel handle form stamped into the blank on one end instead of the normal tang. These have a suitable single and double bastard-cut sides. The double cut takes steel off quickly while the single cut is good for sharpening. If you want a really smooth and sharp edge draw-filing with the single-cut side can put a mirror finish on it.

Some cane cutters wear their handy-file in a simple leather belt sheath so it is always close and their machete stays very sharp.