Folding 3-blade buck for me - My dad gave it to me but I don't carry it daily, pretty much only on the weekends when I'm kicking around the yard, garage, etc. Useful tool as some have said - never really thought of it for self-defense. It has scraped putty, dug out splinters, scraped off old gaskets and gutted a fair number of trout. Awesome knife with a lot of sentimental value. Gave one just like it to each of my 4 boys.

On a boat (besides my kickass bait, gutting and fillet knives) I carry a larger Spyderco with a partially serrated blade with the idea of being able to cut a rope in a hurry if needed. Only needed it when a guest on a friends boat and cutting his anchor line that was all tangled down in the rope locker with the anchor grabbing hold of the rocks without enough scope to ride over the fairly large waves that were about to swamp the boat. He didn't seem to have any idea why all of a sudden the waves were slamming over the bow. Took him a bit to understand what I had just done - he was pissed about his anchor - and a moment or two longer for him to realize it was almost his boat on the bottom instead of just his anchor - thanked me profusely.

Carry that one hiking and camping as well.