From what I am reading by your question I would suggest self defense classes. Carrying such an item could cause you as much problems as it could solve them.

Not knowing nor pretending to know the laws in your area, I will say that you are possibly causing more issues that you are solving.

Perhaps some classes on self defense would be best. I know that there was a bit of shoot out in Toronto recently, and I am not sure that possessing a fire arm would have solved the issue. Ducking and running, that may be at times the best solution.

Even if you do decide to carry, I would strongly suggest self defense classes. You may not be looking to learn Kata's and forms, but a real world self defense class may really help you.

One of my instructors once said, "once you clear leather and pull the trigger, you just committed to $10,000 in legal fees."

Questions of use of force and so much more come into play.

For the urban bag, you can better judge what you do and don't need in there for resources.