Leave your beach towels at home, and save space in your luggage. And the nightmare of trying to get them dry afterwards, they won't dry in your room, and the dryers are $1 for 20 minutes.
The towels provided seem to do an adequate job of drying you off. They are not beach towels, in size I would guess a small bath towel. 38x20 inches is a rough estimate of the size.
Hope this helps....