Check at Wal-Mart (or someplace similar). They actually sell some stuff there that is a temporary fix to put crowns back on. Of course right now I can’t remember what it’s called!!
It’s together with some other teeth cleaning utensils – they actually sell some serious stuff over the counter that dental hygienists are trained to use. Making sure your tooth is dry (use a washcloth or even a hair dryer!!) is the most important thing to watch out for.
Of course, it’s still very important that you go see your dentist within a couple of weeks – they may be able to put the crown back on. But this should be a temporary fix for you until you can get in.