If I leave the house without a knife, it means that I've forgotten to put on my pants. I've carried a pocketknife ever since I was 6 years old. Kids can't do that today -- any kid carrying a knife in school is expelled.
I have about 30 pocketknives at home to choose from, including that very same folder my mother gave me when I was 6. It's old and pitted now, but I treasure it. Most of the knives are pretty ordinary Bucks, Cases and Schrades that I've picked up along the way. The only oddities are a couple of sgian dubhs (the little knife Scots hide in their stockings) as well as a Fairbairn Sykes, Britain's superb and truly beautiful commando knife.
At the moment, there's a little Leatherman Style on my keychain and Leatherman Juice 2 on my belt.