For all Disney excursions they will have bins of towels set up at each of the excursion meeting places which will be listed in your Navigator....the meeting places are usually in the clubs and theatres and lounges....you go to the meeting place at the specified time....you can then pick up towels from the bins provided, you usually have to sign a release form of some kind and the CM's will collect or go over your tickets to make sure everyone is at the right meeting place and the CM's will hand out stickers to place on your clothing to identify you as on a Disney excursion (that correspondes to a sign held up when the CM leads you to the start of your excursion off the ship),
For non-Disney excursions (on your own) you can take towels from the pool area bins on Deck 9....sometimes in port (not always)
DCL will have additional bins of towels set up outside the ship as you get off. They definately have them all the time at
Castaway Cay, but I have not seen them at every single port (I have cruised 13 times and sometimes they do and sometimes they don't) so be prepared and just take them from Deck 9. Do remember to return them. DCL will have a bin for used towels either right outside or inside the ship as you return.
FYI...DCL towels are small...they are about half the size of a regular beach towel...you will probably need more than one per person.
