Congratulations on finishing the book! By now you should be sounding very good and be getting a lot of pleasure from your harmonica playing. To add to that pleasure, and help you practice everything you have learned, there are some extra tracks which have been recorded for you to jam along with. Try out any of the licks in the book with these progressions, and make a habit of improvising your own licks and solos. As well as this, you should play with other musicians as much as possible, as this will help to develop your playing and also put your licks in a musical context.