The sharpest most versatile knife on planet earth, and all for 0.6 oz. I'm really not kidding, this thing is amazingly sharp and useful for everything – from opening bags, cutting moleskin, slicing cheese to hollowing out tree trunks to make canoes.
My brother is really into knives and he told me about Spyderco. They have quite the selection, but this one works best for me.
Available from Spyderco for $15.