If you like doing Sudoku puzzles, there is a web site (link below) that allows you to create your own puzzles specifically to be printed out. You get to select the difficulty and the number of puzzles on the page, and it then creates a PDF for you that you can print out. These are perfect when you are traveling or you know you are going to be waiting at some place. Don't bother buying a book of Sudoku, this site gives you the same thing for free.