Depends on the trip & location...last few trips as examples:
Cozumel (multiple times here): Not much else to do, but we usually take a day to go to Playa and another to cruise the island for drinks & such.
Curacao: Spent a day checking out the island, but mostly diving.
Malaysia: We dove 10 days, then spent 4 days doing jungle treks, river tours, and orangutan sanctuary visits. Ended the trip spending a day in Singapore getting crazy spicy street food in little India, shopping, and then going to the Night Safari (amazing!)
Cozumel (multiple times here): Not much else to do, but we usually take a day to go to Playa and another to cruise the island for drinks & such.
Curacao: Spent a day checking out the island, but mostly diving.
Malaysia: We dove 10 days, then spent 4 days doing jungle treks, river tours, and orangutan sanctuary visits. Ended the trip spending a day in Singapore getting crazy spicy street food in little India, shopping, and then going to the Night Safari (amazing!)