well, if you were interested in becoming physically active they have clubs i.e rowing clubs, running clubs, biking clubs, snowboard clubs etc.
Picking up an instrument to play is a good one too. Lots of guitar stuff out there cheap now because of Guitar hero.
Hiking/backpacking
One I want to do but is really expensive to start is kite surfing. Living in the bay area you see a lot of people doing this, and its fucking sweet.
Pick a goal and work towards it. I.e Marathon, start a band, create a professional website, build a kit car.
Or play video games, though video games aren't really something you work at to promote banging chicks or finding friends, so I'd say if you want to do something productive pick something else.
