Aside from a good tent, a good air mattress (and pump) is priceless. We also found that battery powered fans come in handy during those hot muggy nights.
Packing all of our clothes and such in plastic baggies has been a good thing on occasion as well.
Don't forget the bike! Chain lube and a maintenance stand are good too. We always bring a bottle of cleaner and some rags too.
Have a great ride!