Answer:
i would use the grapefruit and throw it into the water 1 by 1 one leaving sometime in between to see the sharks reaction to it. If they get attracted to it i would throw 1 in then use the bucket to push foward as fast as i can with all of my strength so i can get an equal and opposite reaction from the water to push me foward, i would keep this up for as long as i can. The size of the bucket and the amount of grapefruit were never specified so i would use this for my benefit to say its enough to get to shore
Explanation: