I always (well, most of the times I'm outside my home) have this with me:

I could tell you that I carry it coz "it is recommended for ppl who drive a car etc coz it has this tool to cut the seat belts etc' but I just take it bcoz there are plenty of freaks carrying different stuff like knives etc so I prefer to feel safe. I used to carry a Victorinox when I was younger but it's a sux knife for 'self defence'. This one looks pretty nice(even though it's a pretty cheap sh..). It has that kinda bolt to open it with one hand. There are no regulations concerning carrying a knife in public places so I can take it to the university etc. Well, I just don;t feel safe there