Personal Security is an issue of self preservation, and what you are willing and able to do in the even you are confronted with a life threatening situation.
First thing most people think of is a hand gun or riffle of some sort. That is fine if you have the ability and training that it requires to use a firearm in a hostile environment. So please if your buying a firearm get the training.
There some lethal and less than lethal devices that you can carry that might get you out of a life threatening situation.
Stun Guns, They are extremely effective at close range and legal to purchase and possess in most states. So checking your local and state laws before buying one is a good ideal.
Pepper Spray , Once again extremely effective at close and sort range. I would suggest the more powerful police type pepper spray or my favorite Bear Spray has a 30 foot range and can stop a small crowd if needed. And is legal to purchase and possess in most states. So checking your local and state laws before buying one.
Knifes, Machetes and Axes, These are good to have with you for many purposes, but if your thinking of one of these as your primary self defense weapon. Well if you have the proper training and fiscal conditioning for hand to hand combat you may have a chance.