And as usual there is a holiday themed DLC pack that will be free for the first two weeks or so and then most likely go paid:

http://store.steampowered.com/app/208540/

NOTE: Right now you can't "buy" this DLC. There seems to be a kink that needs to be worked out before people can add it to their accounts. See the Lucky Costume Pack Free, but Unattainable thread for more info.

EDIT: It seems to be installing correctly now.