Feel like your library is missing a something but aren't sure what? Head over to Fort Mason this weekend for the Friends of the San Francisco Public Library Big Book Sale and you'll probably walk out with more than you thought you were ever missing. The sale, held at the Fort Mason Center's Festival Pavilion, will offer over 300,000 books, CDs, DVDs, and books on tape. The festival is free and open to the public and all books are priced at $5 or less. All proceeds from the sale go to the SFPL's various community literacy programs, so your scavenging through stacks will be for a good cause. As an added bonus, the sale will also have the Beat Museum On Wheels parked outside, so if you start to get glassy-eyed from staring at spines, you can take a mini-tour of beat history.