Damone, my old training as a Red Cross/YMCA certified Water Safety Instructor, Senior Lifeguard, and Jr. Lifeguard says WEAR THE LIFE PRESERVER!!! If you fall out or tip the jonboat over you might bump your head on the boat,lose consciousness and drown. The PFD might save you.
If you're going to be boating, you really should go to the Y and take swimming lessons. Anyone can learn to float/swim enough to save themselves.