While the beverage of choice for making havdalah will always be wine, it is permissible to use other liquids. If wine is not available any drink people sip in social settings and is not intended to merely quench ones thirst may be used.
One way to engage a group of young people whom might not be otherwise interested in ritual observance could be to host a service at a local Starbucks, Tully's or other coffee shop using coffee to make havdalah. Of coarse you'll need permission from the establishment. If management is uncomfortable with the indoor flame take it outside. Many coffee shops have outdoor seating; a chilly candle lit night with coffee and friends is bound to be an enjoyable one.
It is possible to keep kosher at most coffee shops as long as you remain informed. For information regarding kashrut at Starbucks go to www.kosherstarbucks.com