Ok. This might be up there with "feeding mayonaise to tuna fish" or "edible paper" (guess the movie reference) but what if you had a rope or chain tether tied to the cooler rack? If you could release the rack from the water then, after you re-board the pwc then you could pull it back up. It certainly wouldn't be easy and you might still lose some gear that wasn't attached but if you're injured in the water...
OR
How about attaching a rope and small buoy to the cooler rack. You could drop it in the water and come back later to find it and pull it back up.
I haven't started drinking yet today...really

