I carry at basic set of allan wrenches and a screw driver. Apart from that if you are taking your bike to some other city, it good to get an inner tube with its necessary components with you. Just in case if anything goes bad. But that's just what I do. You could carry more things with you but it will add more weight and not be good for you. So you have to prioritize what you want to take with you. Read some other responses to know more.