Cozumel is a shoppers heaven. Take a taxi to Dzul-Ha and snorkel. There is a bar that serves food and drinks and they have beach chairs and bathrooms. You can also rent snorkel equip and lockers are available too.

Cozumel offers some of the world's best scuba diving for a reasonable price. Lodging - Depending on your idea of travel, you can find a hotel to fit your plans. I have stayed at the Reef Club, Hacienda San Miguel, and Casa Del Mar. The Reef Club is an all-inclusive resort, which has its advantages. Just be careful, they will try to get you to buy into a timeshare plan. Casa Del Mar is a very simple hotel. It is my top spot to stay as a diver - it is simply a place to rest at night before I hit the boat again. Hacienda San Miguel is near downtown. It is a cozy little place that is quiet and relaxed. Activities - SCUBA diving. I have used Del Mar Aquatics and Sand Dollar Sports. Del Mar is located across the street from Casa Del Mar (hotel). Typically has smaller groups. Sand Dollar has top of the line gear but can be crowded. Food - My favorite place to eat is Ernesto's Fajita Factory. Tons of good food for little cash. Try the Triple - steak, chicken and shrimp fajitas. Plus the beer is cold.

This was a really great city! There is a beautiful square where you can see the bright blue water. It's great for photos.

To get to Isla Cozumel obviously you have to take a boat, you depart from a city called Playa del Carmen that has beautiful beaches and some beautiful little shopping area. If you've come on a tour from Cancun, you'll get a little bit of time to shop in this area prior to departing.
I can at least attest to the condition of the ocean when I went (October). It was brutal. I never get sea sick, yet this kicked my ass. It was only like a 30 min boat ride but it felt like a few hours.  Once on the island, food and shopping are your primary attractions. Shopping was pretty decent, there were some cool little shops. Unfortunately, as this is a tourist area you'll have to deal with tourist-oriented prices with people not all that willing to haggle. No doubt were I not on a tour I would have been able to experience more...I might have been able to get 100% of that horse buggy ride I paid for. :(

Look for shells on remote places. They are the same as in the stores but for free :)

You don't have to go to the mainland to see great Mayan ruins. Take a taxi to San Gervasio park, where you can spend several hours in ancient history.

Don't pay for a snorkeling shore excursion when going on a cruise. There are lots of individuals who will take you for half the price and will take you to less touristy areas, so you will see more fish and less tourists!

CANCUN...IS A PLAYERS PARADISE..... WHY NOT GO UPSCALE...AND VIST PLAYER DEL CARMEN.......ITS...VERY NICE...

If you are staying in Cozumel, take a day and rent a car to drive around the island. The further side is very secluded, and there are great views of rocky beaches. Note that the water is MUCH rougher, so swimming is not suggested. There are small restaurants and shops usually frequented by the locals and not tourists, which are great to stop at the find a 'real' cultural experience at an often over-touristy place.

Rent a jeep and tour the island.