I no longer carry a pocket knife in NYC - too much hassle. I only carry them when I go hiking or I'm out in the countryside. I have had pocket knives since I was a kid.
Buck 110 is my favorite: just the right size, feels good in the hand, classic look; it is my most often carried knife and I keep it sharpened for peeling fruit, cutting cheese & bread on picnics, for gathering porcini mushrooms, cutting rope, cutting and carving saplings to make walking sticks for those hapless 'hikers' that insist on tagging along, etc.
Swiss Army (have a few). I keep one in my camera bag and it has come in handy for tightening screws on various pieces of gear. I used to carry a leatherman for this but found it to be somewhat of an overkill for my purpose.
I am looking for a good folding pruning knife for use in the vegetable garden. I am looking at the Opinel and some others... suggestions are welcomed.
On my belt loop I also carry a Dakota Clip Watch with a magnifying glass and a tiny light - very useful.