Have you seen the "Seinfeld" episode where George brings a book into the bathroom at a Brentano's bookstore and then tries to put the book back on the shelf when he's finished? Hilarity ensues when the store manager forces him to buy the book. "They're selling coffee, bran muffins ... you're surrounded by reading material. It's entrapment!" George says, shortly before he tries and fails in several attempts to return the book.
Don't be like George. Don't take books, documents or other materials into to restroom if others might be handling them later. Would you want to thumb through a memo that you just saw Jerome from Marketing take into the can with him? Just remember the Brentano's sign that George walked by on his way to the commode. "BATHROOM NOT BOOKROOM."
Personal reading material is quite all right, so long as you take it with you when you're finished. Leaving a half-finished New York Times crossword puzzle for the next stall user might seem like a nice gesture, but the paper is likely to wind up crumpled and kicked around the floor.