Spyderco Atlantic Salt- bright yellow. I have it on my person 99% of the time. It is the knife that I will have with me if something happens- my dream knife would probably be an Al Mar SERE variation, or a Chris Reeve fixed blade.
If I go to a formal function, I scale down to a Spyderco Dragonfly, a small Leatherman, or an AG Russell gentlemans knife.