If I am someone's date at a wedding, am I expected to contribute to the wedding gift if I don't actually know the bride and groom? Who is the gift technically from?
How you deal with this actually depends more on your relationship with your date than your relationship with the couple! Whether you know them or not, you are still their guest and the bride and groom are still hosting you, so your name technically should be included on the gift. Unless your date is being really pushy, he or she shouldn't have a problem with including your name -- you are attending the wedding together, and so it naturally follows that you are giving the gift together. How you pay for it is something else entirely.
While you certainly are not expected to get a second gift for the bride and groom, it may be appropriate to contribute to the wedding gift. Your date most likely won't demand payment, but it would certainly be polite of you to offer. If the two of you are more of an item, this should be second nature to you. Another option? If the two of you are attending more than one wedding together, perhaps you can split the costs per wedding -- you foot the bill at your friends' fete, your date pays when you're the "and guest." Then no matter what you've sorted out behind the scenes, go ahead and sign both names on the card.
Registering for Wedding Gifts