The Celestial Omnibus, by E.M. Forster
Unlike many of Forster's novels, this book does not involve Italy, repressed homosexuality or tragedy. It's just an engaging story about a little boy who finds the celestial omnibus that will take you to Heaven, where he runs around with some famous figures and has a nice time. Borders was selling a small, pretty copy which could easily be stuffed up your sleeve; I don't know if they still have them, though. You could also just read it here.
