As the Author that is the major marketing force behind your book - you'll want to have an arsenal of tricks at your disposal for promoting your book. Promotional materials, such as banners, business cards, bookmarks, etc., are a standard part of the well-armed author's bag of tricks.

You'll need a display for your public events, like book signings or speaking engagements. You'll want something to hand out to people, probably with ordering information printed on it. You might want signs to put in public places where readers collesce; places like coffee shops, bookstore bulletin boards, and local writers' group meeting places.

The bottom line is that promotional materials make you more visible, and the more visible you are, the more books you're likely to sell.