Skating and playing hockey are some of the funnest things to do in the winter. With ice rinks around the Bay Area, it's also something that you may have more practice at doing year-round, and so will be ready to hit the ice when you get up to the mountains.
Public skating at High Camp, Squaw Valley in Olympic Valley. It's a pretty fantastic vantage, at the top of the mountain, but it's a mission to get up there...and expensive, so call first and plan ahead.
OPEN: Check first, as their website is not up-to-date this season
COST: It's at the top of the Gondola, which costs $44/adult and $22/kid to get to the top if you don't have a season's lift ticket.