Since you won't be using film most likely, I suggest an extra flash drive or two in case the regular one gets full.
Having shot 3 different Rotary Operations on the C&TS, 1991,1993, and 1997, I can tell you the cold really drains batteries. Of course I was shooting video then, but had at least 8 batteries, cause I had a double battery holder installed on the camera at the time. Thus I had 3 additional sets, and generally went through at least two each day of a 4 day shoot. The hard part was trying to charge them all at night, as the charger took 4 at a time and that was it.
As Russ said, give the amount of time and money, and energy you are putting into this event, springing for a few extra things will insure you get as much photographically as possible. Don't forget the tripod and shutter release cable as they will be doing those night photos in Osier.
Greg Scholl