Lelandjane:
Naturally, much depends upon what your interests are.
If you're really active, almost any of the "watersport" offerings might suit. That is, snorkeling, swimming, beaching, etc., etc. Just read the description of each quite closely, as there will undoubtedly be several which are almost exactly the same. Try to figure out what's different between them, book the one that offers the most.
If you're more interested in history and culture, you'll have many fewer options. Indeed, the most significant excursions will take you to the Yucatan mainland to visit Mayan ruins. Tulum will probably be featured, and it is, indeed, a fascinating place. Very unlike more inland ruins, but still fun.
When I was last in Cozumel in 2007 (actually, on the very same day as we had our very own Groundhog Day tornado here in TV), I took the "Mexican Cuisine Workshop & Tasting" tour. It was a huge amount of fun, and the half-dozen or so of us had a ball, cooking and eating our own lunch. All under the guidance of a very enthusiastic young chef (as older folk, some of us called him a child, but he was, perhaps, 30!) None of us suffered any ills for having cooked our own lunch, and I called it very well worth the $74 it cost me then.
As a frequent cruiser who has just recently completed my 12th cruise, I hope you have great fun on your first one. It is now my very favorite way to travel, and I try to do at least two each year.
If I can help you with individual questions, please feel free to PM me.
SWR