I would skip it, not because he'll spread germs - most likely he just ate something that disagreed with him - but because there will surely be treats there and new foods can mess with a dog's digestion on even the best of days. He should stick to tried and true foods for the next couple days.
This isn't the dog with aggression problems, is it? If so, is he ok to go to these things?
He has never had aggression issues? Him and the cat never got along & had issues but he is fine with other dogs, people, etc. We go to stuff like this all the time.
Oh it must have just been the cat issue that I remembered you posting about.