Always fun to be had. If you like the beach try Chakanaab good facilities and beautiful water.
For something different take a taxi to the east side, it is undeveloped, rugged, and beautiful. A taxi will take you on a tour and stop at a couple of places for something to drink. An enjoyable trip for someone who has visited many times.
For a real treat take a ship's excursion to XCaret, an ecological park on the mainland. We have been twice and each time found it to be very enjoyable. A float through the caverns followed by a walk through the park is an experience to remember. This trip takes all day but is one of my favorites. The ride across on the ferry can also be an adventure, especially if the water is rough.