If you are in a relay, most people use the CamelBak or similar type of water bladder which is contained in a small back pack and has a tube with a one way valve and mouthpiece which comes to the front. The advantages of this system is that you can jump in to the boat very quickly if you are doing rapid changeovers and it stays with you if you capsize. The disadvantages are that they can chafe and rub and also that you are carrying extra weight on your back.
Toilet Breaks
Tendonitis
Paddling Clothing
The majority of experienced paddlers wear paddling shorts and either a Lycra or thermal long sleeved top. I have always used thermals and find it amazing how they can wick the sweat away and provide sun protection, yet keep you warm in winter.
Cotton clothing is generally not advised.