No doubt there are some arcane and highly sprecialized tactics, like vacuum bagging your ice, etc.
My interest is in what works best for the typical boater with a home freezer who doesn't care to put in a huge effort, i.e. jugs vs. bare iceblock.
So- please do some test on whatever aspect you fancy: soaked towels vs. bare cooler, designer ice vs. home froze, whatever. You'll learn thereby, and so might we.
But- choose a single variable and work out a test that sets it apart, while the other factors are the same. Otherwise, you're just pissing out the window.