You should try to get on first and put the book down before the potential whale sits next to you. If you sit down after them and try to jam the book in, it's going to take some serious muscle. If your neighbor sits down and they're normal sized, you can grab the book and start reading, otherwise leave it. Bring a book you don't like as well, you're going to want to discard it after it rubbed up against some ham's side-ass for a few hours.