Noöcosm

I'd feel under obligation to bring something to the party, and since you don't know the person very well any more, a bottle of wine seems like a safe gift. Food might be inappropriate for the nature of the party, or excessively duplicative, but with wine, the host can say, "Thank you!" and put it in his cupboard for later use if he doesn't want to open it that night. Generally, I try to ask when the invitation is issued/received, so that the host can make assignments as needed, but wine's a good short-notice, didn't-know-what-you-needed thing. The only way you can really go wrong is if the host is morally opposed to alcohol, but not even Jesus took that harsh a stand, so I wouldn't sweat it.