If I had to pick, I'd take a carabiner instead of a pocketknife when I hike. That's right, climber's hardware instead of a knife. I can always tear the bread and burn cord in half with a lighter, but how can I attach things? How am I going to make a pulley? Those versatile climber's snap-links -- now there's an essential you can use to:
1 Hoist your bear bag between two trees out of Yogi's reach. Use a carabiner to attach a stuff sack full of rocks to one end of the rope and throw the sack over a tree limb. Attach the sack of rocks to the other end of the rope and throw that over another tree's limb. Before tightening each rope end around the trees, clip the 'biner on the cross rope and slip a second rope (for hauling) through the biner. Pull the cross rope tight and secure it to the trees on each side. Attach the food bag to the haul rope and pull it up on your carabiner pulley.
2 Hang a water bottle from your pack. Clip it to the bottom of your shoulder harness strap, rather than the pack bag, so it won't sway.
3 Hang sandals off your pack for quick access at river fords, and then to dry afterwards. Any often-needed item can be snapped to your back.
4 Create a laundry line for hanging wet clothes outside the pack to dry.
5 Attach to your water bottle, then lower it into a pothole to get water in the desert. Attach it to the bail handle on your pot and heat soup in a hot spring.
6 Rig a Tyrolean traverse-a tight, load-bearing cross rope used for sliding people and gear across obstacles like swift, narrow rivers, or deep, narrow gorges. Use biners as impromptu pulleys in the system.
7 Defend yourself from ranting companions with "brass" knuckles.
8 Clip your car keys to your pack so there's no rude surprise at trail's end.
9 Open drink bottles with the carabiner's notched gate for celebrations when you do get into to your vehicle.
10 Maybe even go climbing.