Sarah, lets look at another possibility before we mention the beach stop.
If you disembark the Adventure of the Seas, with luggage there is a place in old san Juan that can stored luggage during the day for a minimal fee. They are located in front of pier # 2 but your group of 28 will need a cab to get there at about $3 p/p.
Once you check in your luggage, you are in the old city and you can do a few things for starters:
1. go to pier # 2 and take the ferry (about 75) cents accross the bay the a cab in to the Bacardi rum distillery (about $2 p/p cab ride)
No entrance fee at the distillery but there is a tour and some rum tasting
how`s that?
That whole time process can take about 4 hours.
Then you will be back in old San Juan for lunch.
There are many places to go to from a burger king to
Restaurante Raíces
2. after checking you bags, there is a trolley (free) that takes you to the two forts entrance fee ($5p/p for both) or one for $3
That process can take about 3 hours
In other words Sarah, take advantage of the second oldest city in the new world.
Now the beach option:
After checking your luggage take a cab to Escambron Beach. It is the closest beach from the storage area and its also the closest to the ship.
Its also about a 30 minute walk along the ocean, if you like walking.
You can take a bus there for 75 cents correct change
One more option that just popped in, how about going to the airport storing your luggage there.
More information on the next message.