Unlimited Chainsaw Fuel
Hold L1 and press X, X, Circle, Square, Circle, Square, Triangle at the main screen.

Wolverine troop leader killing
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.