I wish I had a photo to show you the sandwich I ate waiting for the Fire Island Ferry from Willie B's (631-206-2580 at 222 Fifth Avenue, Bayshore, NY). Nice, tender, fatty (in a good way, to the overly health conscious), chunks of well smoked second cut brisket, a smokey, tomato based barbecue sauce, and two sides: collards and beans, both of which were quite good. I ran into a friend at the ferry: she agreed with me completely about the brisket, and also told me about her excellent takeout experience at Willie B's as well. I personally haven't eaten enough to give it a full review, but it seems to be a no brainer to or from the ferry.
You can call ahead from the car and place your order for pickup as you head to the ferry. The man I spoke with in the store said that they will deliver to the ferry (Bayshore side) as well. They also sell Willie B's at the Inn Between (in Ocean Bay Park) on Friday nights. Willie B's is takeout only.
Please let me know what you like and don't like if you stop at Willie B's.