I think the notion of carrying a knife for protection is rather silly, not that it cna't be used for protection however I would venture to bet 99% of people who carry a knife and think it's protection have no idea how to properly handle a knife or use a knife in a self defense situation. Alot of knives people carry for "self defense" are more slashing weapons than stabbing but I bet most people would try to stab and probably wind up cutting their own hand up more than the offender they are going after.
One toher thing I would recommen not carrying a knife out drinking. We dont always have the best judgemetn or make the best decisions and oftentimes a situatin that could just be a fistfight turns into a murder or assault with a deadly weapon and even if you are in the right if your drunk you'll probably be said to have been aggressive, not in the rigth frame of mind, etc.
Depends on the state. It has been argued that buying such a thing makes it a striking weapon (and thus higher charges if brought, since it shows intent to use as a weapon) rather than a weapon of convenience.
The best baton is the good old Millwall Brick.
I've been carrying a knife since my boy scout days, which was a LONG time ago. Knives are dandy weapons, and in fact, are one weapon that can be learned more quickly than just about any other, and are an excellent force multiplier. I've taken several knife fighting courses, and highly recommend doing so if you are going to carry one for self-defense purposes. This should also include learning your local laws so that you know exactly when you can legally use it to defend yourself.
Look at Hank Reinhart's Book of Knives. It is a very good reference of the use of knives. Probably easiest to find it as an ebook from Baen Books. Try baenebooks.com.