Yes, you can buy duty-free alcohol in the onboard shops on Royal Caribbean, but there is a major catch: you cannot consume it during your cruise. When you purchase a bottle of liquor at the "Port Merchants" shop on the ship, the crew will securely store it for you and deliver it to your stateroom on the final night of the voyage (usually after dinner). This policy is designed to encourage passengers to purchase drinks at the ship's bars or through pre-paid beverage packages. Similar rules apply to alcohol purchased in port; if you buy a local bottle of rum in Cozumel, security will take it from you as you re-board and return it on the last day. While the prices are "duty-free" and often lower than what you’d find at home, you must factor in your home country's customs allowances when bringing it back. For US residents, this is typically one liter per person, though additional bottles may be subject to a small duty tax upon arrival.