Screw Driver, Knife, Scissors, Air Horn, Phone with Three Words App to give precise location to Emergency Services.
You need somebody to remain calm, the injured party does not want to hear, Oh My God look at that cut, or that bone sticking out of you leg, shock and panic can Kill !
First make sure the airway is not compromised, keep them calm and breathing to a rhythm, Sit on the platform with your legs under the injured persons arms , until help comes, you could make things worse trying to get them on the boat.
Call somebody closer if the Emergency Services are going to be a while.
Depending on the severity of the injury and I am thinking arm through the handle, if they can get in the boat, get to the dock dump everything, put them in a car and head straight for the nearest hospital, there are some main arteries under the arm, that could spell Danger if damaged..
A good skier that has been talked about on this forum and endorsed handle guards, actually died twice on the operating table, they waited for emergency services that didn't, show up for a couple of hours, fortunately after 1 hour somebody made the decision to put him in a car and take him to the Hospital, that person saved his life.