Half-Moon Cay, Bahamas: Known by Holland America and Carnival cruise lines as Half-Moon Cay, this small island is officially called Little San Salvador Island, Bahamas. It is a day-at-the-beach kind of island, and leased by the cruise lines for private use. The island features all sorts of water sports, including swimming, snorkeling, parasailing, jet-skis, and so on. There is also a small market in the main complex.
The island has no dock, it is only accessable by tender, and it is not uncommon to have more than one ship in port. We have been there once in 2012 when we cruised on Holland America's MS Zuiderdam.
The ship's crew brings lunch on shore and cooks a traditional beach cookout, with burgers, hot dogs, and barbeque offerings. It's intended to simply be a relaxing day at the beach, and it certainly lives up to that goal.
Half-Moon Cay is a hidden gem. The water is crystal clear, and the beach sand is white powder - and you just want to burrow your feet into it. It is one of the best beaches in the world in my opinion.