A solid third of the 3,000 people aboard the MSC Poesia cruise ship are here to pack their days with yoga, meditation, and lectures on emotional purpose and physiological prevention instead of the all-you-can-eat, drink, gamble, spend, and sunbathe pleasures the rest of the passengers are pursuing. Since Holistic Holiday At Sea launched in 2003 with 300 paying participants, its client list has nearly quadrupled.