Why bring one? I don't know about you but, I find it kind of hard to pack my stuff when there's a huge gash across my pack.

What kind should I get? You just throw in a needle and some thread. You can make a dispenser very easily out of a floss dispenser. Just use all on the floss and find a part that will allow the center part to be removed. You can normally pull the dispenser apart or use a screw driver to pry the center out of the dispenser. Then you take the little wheel out and wrap about five feet or more of string around it and replace it in the dispenser. You can slide a needle into the hole where string comes out. Duct tape is also helpful. It will repair almost anything. You also want some wire and some rubber glue.