Luquillo beach is about an hour East of San Juan and about 15 minutes away from the El Yunque Rainforest. There are excellent facilities there including for the handicapped. The water is usually very calm.
This beach is a favorite of the locals, so if you enjoy getting to know Puerto Ricans, talking with them about their country and cultures...this is a definite must!
Another plus...this beach is crescent-shaped, edged by a coconut grove and beautiful! If you were to look left of the tip of the crescent, you would see the neighboring island of Culebra.
Equipment: Swimming and sunbathing gear....duh.... and a friendly attitude! :))
This is probably one of the most intense exercises you can do down here. Find a guide and get goin on a 20 mile trip around small islands that are around a few key beaches. I'm pretty sure it's not that expensive -- you could always just rent a kayak for the day and attempt it yourself if you are so inclined, but I wouldn't say it is a beginner sport!
Equipment: A kayak is key here, also the paddle. You need to be able to get around in the water.