A knife to me is for cutting boxes, opening letters, and the like. I have something more technologically advanced for self defence.
I almost always have a little S&W "California Issue" automatic knife in my pocket. The blade is about two inches long, the scales are anodized aluminum. Another favorite is the original Leatherman, a SwissArmy, or a CRKT Crawford/Kasper. I also carry a variety of BenchMade folders, or at times a little fixed blade belt knife by
L.O. Albach. The sheath lays parallel to the belt, I wear it up by the buckle on the weak side. The knife is held by the molded leather sheath, and a quick crossdraw pulls it.