One pair for formal night
One pair for poolside and deck (sandals). It will be better to use a sandal that have straps or something that holds your feet, so you can use them for excursion and walking around the towns
One pair for casual nights
If you are planning to go to the caribbean, well the decks get pretty hot. Especially the stairs by the pool side and the parts were the deck is like cement, or something like it. They get pretty hot, and you must run in these area if you dont want to get a burn.