anyway my reply may be too late. But who knows my post would still be helpful to somebody else.

Dante had already enumerated the most important things needed. In addition I suggest you bring a water-proof camera ( i don't know what else to call it). You may see things along the river that might really interest you and you find it beautiful. A friend of mine who was rafting in a class 1 river, once saw a bird he have never seen before, its one of a kind. Only to find out after days of researching that its already considered as extinct species. If its extinct, how could he able to see one?