At this point all I really have is the start of a list of items we will need. I will in the near future work on a basic itinerary for how long it will take, miles per day, and places to visit and/or overnight. Things that have made the packing list so far:

Clothes for 1-week (will probably do laundry at some point)
Gas for 250 (?) miles
Tires good for 2,400 miles (one-way)
Water/Camelpak
Food for 1-day
Camping gear
2 pairs of gloves
2 visors for helmet
Neck protection
Riding suit (Aerostitch, BMW Santiago, etc.)
Rain gear
Riding boots
Comfortable seat
Motor oil
Tire repair kit
First-aid kit
Tools

For long distance trips on a bike storage space for gear can be a problem. My bike has some small hard-cases that mount to the rear, and I will be purchasing a tank-bag to complement a large bag that straps to the rear seat area. On top of that you can strap tents, duffel bags, etc. For bikes that don’t have hard-case options, there are plenty of different cargo systems out there that can be made to fit, from after-market hard cases to soft luggage. Some examples here. Since we will probably not be very far from food/lodging at any time not every bike will necessarily need to carry camping gear, tools, etc. Once the group is set we can determine who will carry what gear for the rest of the group.