If you go to the Tomales Bay Oyster company, make sure that you bring everything but the oysters. I learned that the hard way, as we were caught with no drinks, side dishes or equipment for shucking oysters. Next time I will come more prepared.
On the bright side, if you don't eat the oysters you can just explore around Tomales bay, which is not a bad alternative. At low tide you can see all kinds of fun remnants from the night before.