Well there's the beach....
And I'm pretty sure Carmel and Monterey are nearby (about an hour?) Like I said, I don't know that area too well, so I don't know what's close by. But there's plenty to do if you're willing to drive an hour or more.
And it sounds like you're set on going to SCBB, but there's always Marine World in Vallejo if you change your mind, which has Napa and Vacaville nearby. Of course that would mean wineries (ugh) and outlet shopping, and I might be wrong, but that's probably something you personally don't want to do.