Short, fun, easy read; classics preferred

Hi – I'm looking for a relatively short, easy read for an upcoming bus trip. I've been trending towards classics lately, but if you've got something really engaging that isn't a classic, I'd still be interested. I don't want anything too heavy or depressing. No tragedies or melancholy tales of heartbreak. For example, Frankenstein was a good read (though a little on the tragic side). If there's a good collection of classic short stories that fits this bill, that would also be of interest.