As mentioned earlier in the book, it is a good idea to learn a bit about guitar or keyboard playing in order to improve your all round knowledge of music. Being able to play one of these instruments means you can also accompany yourself when you play harmonica.
There is a device called a harmonica rack which holds the harmonica and fits over your head – resting on your shoulders, thus leaving your hands free to play guitar or keyboards. Many singer-songwriters (e.g. Bob Dylan and Neil Young) have used harmonica racks to give them more options as a solo performer.
Most music stores which sell instruments carry harmonic racks or can at least order them. It takes time to learn to play two instruments at one, but like everything else, it is simply a matter of practice. Start with simple melodies and rhythm parts until you develop some basic co-ordination and you are on your way.