Unlimited chainsaw fuel:
     Hold  L1 and press X, X, Circle, Square, Circle, Square, Triangle
at the main screen.

Killing the wolverine troop leader:
     To  kill the wolverine troop leader you have to run to one of the
four  poles  that  are around you and the leader will follow you. When
you  get  to a pole and the leader is behind you, hit the pole and the
rocks  will fall on him. Do this until he is killed. Now go to the big
pile of stones to leave the area. This will grant you the archery key!