I like 2-3 depending on what I'm doing, unless I'm going to a public gathering, then I can sometimes carry up to 6.
My reasoning?
First let me tell you what I carry:
1 locking blade
1 SAK Tinker
1 Leatherman WAVE
That's most days. The locking blade is to cut things...most things. The Tinker is in case I dull the locking blade on something and need another, as well as the many tasks it can perform on its own. (I use the toothpick daily).
The WAVE is for when I know I'll be doing something job-like. (fixing a car, assembling a bed, etc) I carry it and the 30(?) bit driver set. Keeps me pretty well prepared.
For social gatherings or public events where I'm not getting metal detected or frisked:
1 locking blade in pants pocket
1 locking blade in jacket pocket
1 SAK Tinker
1 Case Trapper
1 Opinel No. 7
1 Balisong (if legal)
The redundancy of the locking blades in pants/jacket is for changes in temperature. Sometimes I take the jacket off, otherwise it's easier to reach into my jacket pocket.
The Case is for when I want to keep a low profile. In Texas, Case is king, and will never get you funny looks.
Tinker is for same reasons stated above.
The Opinel is like a "Just in case I need to slice something really thin" occasional knife. I also hand it to people when they need to cut something because I'm not worried about it, and it's funny to watch them try to figure out how to open it. (;
The Balisong is for when I get bored and I'm around friends who know I'm not going to fillet anyone. I like to flip.
There ya go.
