[captndale]

If I were to carry only one knife it would be a medium-sized steel tool with a blunt end. It would have a line-cutter notch in the blade and a serrated back. It would have a sheath from which I could extract it with a minimum amount of trouble, yet it would be secured from accidental loss. I would carry it on my waist strap.

A blunt end is useful as a screw driver and as a pry-bar. If you hunt, you may prefer a knife with a point. I have never found another use for one.
A line-cutter notch is useful for quickly cutting wreck or cave line as well as monofilliment and can also be used to open bottles of your favorite beverage.
A serrated blade is often, but not always, better to cut larger diameter line. I like to have both a smooth, sharp edge and a serrated one.
The placement of a knife on the waist keeps it out of the way, yet in a position in which it is easy to access with either hand.