Other people's hands. This method of catching the flu is so obvious that we don't think about it. But if you want to stay healthy, don't touch another person's hand for any reason until Easter. If you're at a party where handshaking is a social necessity, keep a drink in your right hand to discourage people from offering to shake. Come to think of it, this is good strategy whether it's flu season or not.
Money is plain nasty.
This is no accident. Stay away from money, or better yet, send it to me for safekeeping. Maybe you think you're already careful about doorknobs. You grasp the doorknob to leave, totally reinfecting your hand with, among other things, flu germs. All those wadded towels on the floor prove that other people are doing this already.