We had a discussion at lunch regarding the safety and legality of drinking beer while rafting (specifically, but could apply to kayaking as well). The laws by state may vary, but generally speaking, I believe it's illegal to have open containers in motorized boats (ski boats, etc like you'd see in lakes and resevoirs) within reach of the driver of the boat. For those types of water craft, it's pretty obvious as to why, it's a safety issue, just like drinking and driving in a car. Those are all motorized though, while most water craft on the rivers are not.
Is there any law that applies similar logic to rafting or kayaking?
As far as I know, it's actually more of an un-written rule that you must have beer WITHIN reach of the oarsman/guide of a raft...