Bring food and beer. And maybe a pillow. But mostly feed and importantly, not 3.2% ABV beer. This can be purchased readily in most places outside of Utah.
Obviously it's gonna be chilly. Pack for riding in 30-50 degree riding weather. Gloves, tights, a sick flannel lumberjack shirt. And if you've got 2 pairs of mountain bike shoes, bring both. It sucks riding two days in a row in wet shoes. You get the picture.
Bike: you're going to be riding one. It's probably gonna break. The better you prepare for that, the less likely it's going to happen. Bring a tube, and you won't get a flat. Know how to fix your shit, and you likely won't have to.
The riding in the valley is going to be excellent. Higher elevations will likely be a little snowy. There are lots of trails that I haven't ridden in Moab that I would like to try. One suggestion from Zack is Pipedream. It's right in town and it looks fun for all ages.
The entertainment committee will decide on the off bike competitions on Monday. Mark your calendars and prepare for a trip to goodwill. I hope we get to use hot glue.