Wouldn't really class this as useful or even a skill but I have learned some pretty awesome card tricks with normal decks of cards. Always had the 'woooooow how did you do that' response every time I've done them. Good thing about cards too is that there's always a deck lying around. Quick to learn and easy to do.
Useful skills I'd say learning some of the language, car mechanics, cookery etc but they have already been mentioned.
[ Edit: Edited on 28-Jul-2009, at 09:51 by pazz5 ]