Just rember to return the used towels back to your cabin and your cabin attendant will leave fresh ones for you, if you don't return them, they now charge for the price of a towel, so watch those towels!
I bring my own inexpensive beach towels. I hate to feel like I have to watch my towel or be charged $25. I lay it open in the bottom of the suitcase, pack my clothes and then fold the ends over. It really doesn't take up all that much room.
Do you know does RCCL give you towels when you leave the ship in port - on disney they handed them out and there was a bunch at the pool in a couple areas - do we just get the one per person per day - with kids this could be interesting.
Your cabin attendant will leave clean pool towels each evening for you, profided you leave the used ones in your cabin. You can also take them off the ship for shore excursions or going to the beach, but be sure to return them, otherwise, you will get charged for the price of a new towel.
On the Vision of the Seas in October they had an attendent by the pool and you could exchange your wet towel for a dry one there. Even if we were done swimming for the day, it was nice not to have to have a wet towel lying around the cabin while we were trying to get ready for dinner.