Common types of accessories for your bong include things like ash catchers, down stems and cone pieces.
Ash catchers, which are sometimes called pre coolers are one of the best accessories you can add to a glass bong.
Ash catchers will filter out much of the debris and tar before it it reaches your bong, therefore reducing how often you will need to clean it and also keep the water cleaner for longer.
Down stems and cone pieces are things you may need to replace from time to time, but you may also just wish to try something new or different.