I'm really suprised there aren't a lot more posts about how a knife saved someone's bacon.
Me:
Shaving firestater tender in weather that simply would have never permitted me to make a fire in life critical applications (half the group was very hypothermic and we were in wet whiteout conditions).
Spearing / cleaning frogs, fish, other wild game
Cutting away clothing on a trauma victim (while hiking found a motorcyclist who slid off a cliff).
Preping bandages / moleskin
Cutting tree limbs to custom fit replacements for broken pack stays
Keeping safe in a rather threatening human element situation.
Tightening slotted head screws that held together an external pack frame that fell apart.
Cutting a trash bag open as an improptu shelter fix when our rain fly seperated from the tent and blew away during a major storm (cheap tent, go figure).
Lancing blisters & splinter removal
I'm sure I'm forgetting far more than are listed here.

