Wear some kind of sandle-Tevas are ideal. A hat is a good idea as well. You never know if the river is running slow and a 2 hour float can turn into 6 hours. I bring an umbrella as well for the times it feels like my skin is cookin'
Toiletries and Medical Supplies: Sunscreen! Make sure it is waterproof-not water resistant. The best kind is the kind you don't have to rub in. Spray on is better because you have no towels to dry your hands to rub it in. 40 SPF+
Photo Equipment: Waterproof camera-after several hours drinking on the river, someone is bound to get naked, throw up or otherwise make a fool of themselves. Document it!!
Camping/Beach/Outdoor Gear: Bungy cords or rope to tie tubes together
Miscellaneous: Bring some waterproof baggie to hold smokes, lighters, money and anything that should not get wet. Be sure to make room for some H20 and food in your cooler!
Sunhat, shoes that you can get wet, swim suit, sunglasses.
Toiletries and Medical Supplies: SUNBLOCK - You'll be out on the river in full sun for about 4 hours, possibly more, so if you burn easily bring a high SPF sunblock.
Photo Equipment: A waterproof camera would be good. Make sure it has a string so you can tie it to your tube.