It is a good idea to pre-book that mat, they do go quickly. You can also use it in the water and on the beach. There is lots to do there, but if you want to just lay on the beach, thats one of them.....have fun! They do serve a nice BBQ lunch, so be sure to get some food and you'll be able to get drinks using your sign/sail card, there will be waiters selling them on the beach.
Bag the mat...Labadee had plenty of comfortable beach chairs. A small tip and we were set up just feet from the water with 5 lounges. Spend some time at the waterpark instead - it's a blast (and exhausting)
Yes, plenty of lounge chairs and some hammocks as well. YOu can also rent a water mat to use in and out of the water. I found them great for the water, so nice and relaxing. You can pre-book them or use your TV in your cabin to reserve one, I think they were $10.00 for the whole day.