Best Of

@mertesn said:
Until it hits the ground. A boxer on the ground is like a turtle on its back.

If you've got the money and are so inclined look for security training companies in your area and get a Use of Force License (If it works the same way as up here)

They'll teach you how to defend yourself provided it becomes necessary (As @Mertesn said it's a last resort, regardless of training) in the use of a baton or sap.

Do not get one until you've either taken a UoF class or self-defense classes.

On that note, Boxing is not particularly difficult to learn the basics for (Provided you take classes) and is a rather pragmatic, efficient martial art.

The only true self defense is not being there when the attack arrives. A weapon will only serve to increase the chance that you get hurt.

@Tushon said:
Tools are only as good as the operator. Not getting into a situation is better than trying to get out by show of force without the skill the back it up. My recommendation is to get practical self-defense training if you're consistently worried about your safety.

This ^^^^^^

Nick's free five minute self-defense seminar:

In any good self defense program you'll learn that one of the first things is to carry yourself in such a manner that you project confidence and awareness of your surroundings. If you look like a less than easy target, you'll likely be left alone. Look and act like a helpless and unaware chump and you'll likely be treated as such.

The second thing is to keep yourself away from likely locations of something happening. It's not always reliable, but it certainly helps.

Actual physical self-defense is ALWAYS a last resort because it means engaging your adversary and the odds are high that you're gonna get hurt. If you aren't properly trained in the use of a weapon, you shouldn't be carrying it. It'll get used against you. That knife or baton you pulled out thinking it'll be a deterrent? Guess what, the bad guy just took it from you.

Bottom line: regardless of your weapon of choice (knife, stick, gun, hands/feet, whatever), if you don't know how to use it efficiently and effectively, you're fucked.

Tools are only as good as the operator. Not getting into a situation is better than trying to get out by show of force without the skill the back it up. My recommendation is to get practical self-defense training if you're consistently worried about your safety.

As for you specific question:
My personal inclination would be that a standard pocket knife would be useless for self-defense, because in any situation in which you felt the need to use it, pulling out and opening up a normal pocket knife would not happen. If you are using something like this HK assisted open, that's different but still not advisable as you're more likely to have it turned against you if you don't get some training. A baton is easier to use without training than a knife, but you should still invest in a more holistic self-defense class that includes weapons training if you're worried.