What about Duty Free Liquor and Cigarettes

If you buy any liquor while onshore, the ship's security will take it from you at the gangway and give it back to you before you disembark.

If you buy Liquor or Cigarettes on-board, keep the slip and keep the purchase within the limit of importation of your return country. Most of the ships will supply a list to customs of all the passengers that have bought goods in excess of the limits.