My Tailgate Party ideas are published at celebrations.com. I chose the Oakland A's colors because my family would want that. We've had some fun Tailgate Celebrations in that Oakland parking lot over the years.
You could probably adapt this Tailgate Party for a Giants game...It might not be as much fun, but you could try! :)
I also made these sandwiches for a "finger food" party and cut them in about 2 inch squares. Weighting them and pressing them helps them stay together so well.