A cylindrical, ceramic rod or extremely-blunted, fine, rat tail wood file, under very light pressure, can be used to sharpen a curved blade, razor sharp. Fine sand paper could be used between the finger tips, or over the edge of your finger, if you are very disciplined. The paper, without grit can also be used to create a fine edge. Clogged, belt and drum sanders would be physically possible to use, but I would be very apprehensive about ruing a better knife. There are also wet stones, shaped like spheres, held between the fingers.
All kinds of literal garbage can be used to cut bark and hold scionwood, but it is also good form to sterilize the knife, as for surgery.