Dagger's Blackwater 11.5 is such a boata cross between a whitewater boat and a touring model. A little less than 12 feet in length, it's got enough room for gear, paddles reasonably well on calm or flat water, but can handle up to Class II whitewater. Mind you, it's not going to be a champ in whitewater, but it'll get you through it! And at $700 it's not too hard on the wallet (www.dagger.com).
Wilderness Systems' Pamlico 140 ($650; www.wildernesssystems.com) is slightly longerabout 14 feet, as the name impliesso can hold a little more stuff than the Blackwater, yet still offers that flatwater to Class II flexibility. This too would make a good, versatile boat for your trip.
Now, a good kayaker can handle rougher whitewater than Class II in one of these boats, but don't press your luck. The extra length of these boats makes them more difficult to steer in tight quarters, increasing the risk you hook a rock or something. They also provide a longer "lever" for water to grab. Don't mess with fluid dynamicsyou'll lose every time.
For more river-runners, check out Outside Online's Kayaks Buying Guide.