I don't carry a back pack, but often have my possibles bag. I modified the bag to carry a small field axe. Ignore the Dunlop in the photos below. 
Vaughan sounding axe.
Field carry.
Wetterlings wildlife hatchet.
Field carry.
Wetterlings small hunting axe.
Field carry. This is about as long as the handle can be for convenient field use.
Vaughan sounding axe.
Field carry.
Wetterlings wildlife hatchet.
Field carry.
Wetterlings small hunting axe.
Field carry. This is about as long as the handle can be for convenient field use.