One thing that's helped me is to always keep copies of my two books in the back of my car. Then when someone says "Where can I buy a copy of your book?" you can tell them they can get it from you right then and there.
Also it helps to have business cards with you advertising your book. One thing I have tried is tacking one up on any bulletin board that seems friendly to local businesses. Does it help sales? I have no idea, but it can't hurt, and the card costs me only a penny or so. Sometimes people will come up to me at a book signing and tell me they've heard of the book but can't remember where. Just getting your name and the book's title out there is helpful even when it doesn't result in an immediate sale.
