The free items, including a coat and winter hat, are automatically unlocked after signing into Xbox Live. New selections are designated by a yellow star in the Avatar Creator Tool.
It's the first clothing update for the customizable avatars, which arrived as part of the New Xbox Experience on November 19. Microsoft has stated plans to release new items across the next six months, though it's not known if all the parts will be free.
An avatar parts store is slated to eventually hit the Xbox Live Marketplace, and will sell various avatar-related items at unknown prices. In addition, future Xbox 360 games may provide new game-specific avatar parts by earning and unlocking achievements.