I can only get it down to four.
Flip flops for pool
Neutral color sandals that go with everything.
Black strappy dress sandals
I think on my first cruise I took 10 pair. After 13 cruises, I have the whole packing thing down to a science. I also am a strict follower of the "when in doubt, leave it out" rule.
I am taking only one suitcase and my rolling backpack (as carry on) for my 12 night Hawaii with precruise 3 nights in Vancouver.