Insurance card and driver's license (or copies). Should always carry:

Flat kit (2 tubes, tire levers, pump or CO2)
Food (nothing new on a long ride; I like Mojo bars, PB and J and bananas)
Gatorade (2 bottles worth) and gatorade powder in your favorite flavor as you will need more)
Bike shorts with gel chamois (but again, don't wear a new pair; what if they rub?)