1. Ask what they're drinking
2. Ask how they know the host. Whatever their answer is, it'll probably lead to another topic. Like if they know them from work, you can ask about their job. Or if they know them from college, you can ask where they're from.
3. Talk about the food or the music. Something like, "Are you sick of all this Christmas music yet?" might be a good line. There's only so much you can say about the food or the music though, so be ready to shift into another topic.
4. Ask what they're doing for the holidays. It's a great go-to question right now, because we've all got plans. And we're either excited about them, or ANNOYED about having to travel and deal with family.