Besides what to carry on the boat every person should have on their person a knife, as much parachute cord as they are comfortable carrying and a fire starter. This is extremely important on wild water. If someone goes over board, or the boat is swamped, each person can take care of their self. Good chance you will be separated from your boat mates.
I like to carry a magnesium fire starter. You don't have to worry about it getting wet. It is light and works well.
Magnesium Fire Starter, Doan is the best