rfamilycruise:W are interested in private excursions in Costa Maya, Cozumel, Belize City, and Nassau.
The best thing to do is to hop on google and look up 'shore excursions [your port]' and see what you get. There'll be a few excursion outfits show up out of the many hits.
We are also interested in what to do if you don't go on excursion, like beach/shopping, etc
Nassau: quite a lot. Nassau probably has a tourist info web page.
Cozumel: definitely quite a lot. Cozumel has several such tourism web pages.
Costa Maya: is very small, unsophisticated and relaxed. Not so much to do for wild partiers except hang out in the dedicated cruise mall. Majahual is a short walk down the road if you want cheap beer on the beach.
Belize: has more shopping than it used to, but it's not a place to be caught wandering around outside of the port area without an organized group.
Desperately seeking 10th cruise for the free laundry.