When I can't carry a gun what I carry is, less money than it would be worth someones time to steal. Though, I carry that when I do have a gun too.
Also, I guess a pocket knife - though the prospect of getting in a knife fight seems less appealing to me than throwing someone my wallet.
Like a lot of other people have said, I think attitude's most important - just be a less appealing target than the guy a block behind you, and you'll be all set.
This thread actually raised some questions for me.
For those of you that carry multiple knives: Is the plan to use more than one at a time?
Having been in a fight or two - though thankfully never one involving knives - it seems like keeping a hand free to grab your attacker with would be a good thing. It also seems like having something sharp attached to both hands at the same time is just asking to cut yourself.
Or is the idea that if you have a knife in every pocket one will always be in reach?
On that front, I just have a hard time imagining a place that I'd have better/faster access to than my front right pocket. Also I'd be worried that keeping a knife in the same pocket as my phone would risk scratching the screen.
I'm trying hard to keep an open mind to the idea, I just can honestly say I've never felt the need to carry more than one knife - at least when I'm not hunting.
si vis pacem para bellum