Take your knitting. A book signing is an excellent opportunity to accomplish a lot of knitting. Having some handwork gives you a neutral topic to discuss in case people want to talk to you but are reluctant to be pressured into buying the book. If it ties in to the book, so much the better! My protagonist works her sorcerery through her fiber arts, and the books include patterns, so knitting is a no brainer.
Unless you are already famous, there will quite possibly be spells during your book signing when you are waiting for an adoring fan, or an interested customer, or even a chatty nine-year-old to show up. Book signings can have lonely spells, and knitting helps. People say to me, "I don't have the patience to knit." I shake my head in puzzlement. If I didn't have my knitting to keep my patience, I'd kill somebody.