Frank Lundeen of Cyclova XC put together a useful check list for when you are on the bike. Cyclova XC will also have some basic bike consumables (tubes, chains, quick links, etc) for sale should you burn through your tubes on in the 1st day.
I also put together a short opus on using a GPS to navigate on the bike on my personal blog.
Water: Anytime you see a sign for a campground there is a good probability that there will be well water available. I will always have at least 20 gallons of water and ice in the truck.
Aid stations: On stages 2 and 3 I will be on course near Isabella with all sorts of beverages and food. There is also the Trestle Inn on the last stage (just before you start heading up Heartbreak!).
Let me know if you have questions