LOL!! We went on the horseback riding tour while we were there. WandA's suggestion might sound silly, you would think people would know to bring something other than shorts. But one girl in our group I don't think had ever seen a horse. Showed up in high heels and looked liked she was headed to the club. She ended up off her horse by the middle of the tour. Just bring good shoes and pants/capris and you will be good. The tour desk will have the options for you when you arrive. It is just a short drive from the resort. The atv tour the have there is amazing also, you head out from the same place but take a different trail.
Does this cost extra? I know its not one of CSA's normal inclusive activites...
We did the ocean horseback riding while staying at CSA in May 2008, and it was a bit different than I had expected but still an unforgettable experience. I think we paid $60 each, plus a $10 tip to each of the guides and another $10 tip to the cab driver (so $150 total). Took about an hour, with maybe a 30 minute cab ride each way. So plan on at least 2 hours, maybe 3 if there are other couples on your tour (we were the only couple on the tour when we took it.)
The reason I say it was "different" than what I expected is that I was expecting a ride through the Jamaican mountains, then down to a sunny ocean surf which we would ride through and splash around with the water up to our knees or so.
In actuality it was a level ride (no hills at all) through a farm/plantation, with the guides pointing out various plants, crops, and animals along the way (the sand crabs were especially memorable as they scattered to avoid the horses!) After 15-20 minutes we arrived at the ocean, which was totally secluded and private with not another soul in sight.
Imagine our surprise when our guide said he needed to put the "water saddles" on the horses! While he did that, we changed into our swimsuits in a public restroom nearby. Then, we rode those horses right into the water, until it was over their heads and they began to swim! We also took photo of ourselves standing on the saddles out in the water!
If you've never ridden (rode?) a swimming horse, it's an unforgettable experience. You can actually sense them paddling like a dog beneath you! My wife still talks about it two years later.
If you provide me with an e-mail address, I will forward to you an e-mail that I received from another poster while I was researching horseback riding prior to our last trip. The e-mail recommends a horseback riding company that gave them an enjoyable experience. We ended up not doing it, but they highly recommended it and included contact information.