You should be ready to go out of the box. Ours came with batteries for the remote, but I bought a charger and rechargable batteries since I'm sure it will get a workout on Christmas day.
There's a great Q&A thread here http://www.disboards.com/showthread.php?t=1287560
with a lot of good info on the system and games. It was also suggested that you test run before the big day to make sure its all working smooth.