According to IGN, nothing, even disc based games, will work without a mandatory day 1 update. While not exactly surprising (The PS4 will have a day 1 update as well, as did the Wii U) it certainly puts a damper on things when you have to sit around and wait.
http://m.ign.com/articles/2013/11/08/xbox-one-needs-mandatory-day-one-update-to-do-anything
http://m.ign.com/articles/2013/11/08/xbox-one-needs-mandatory-day-one-update-to-do-anything