Even the least sensitive skin can develop a reaction to a sunscreen used repeatedly. Make sure to bring several sunscreens with different active ingredients (zinc oxide in one; oxybenzone in another) so you can rotate. You should also have a comfortable hat to wear in the sun and a pair of sunglasses.
While on a Mexican cruise, you will be fine drinking the water on the ship. But when you take a shore excursion, you might want to bring water purification tablets just to make sure. Polar Pure Water Disinfectant, sold at Amazon.com, uses iodine crystals to eliminate water-borne pathogens. The SteriPEN hand held Water Purifier, also at Amazon.com, uses UV light to destroy viruses and bacteria.
Wash your hands. Since the swine flu epidemic, hand sanitizer has become ubiquitous, especially on cruise ships. But on shore excursions, you might not see sanitizer. Carry a small bottle of liquid hand sanitizer or towelettes, and use frequently, particularly after bathroom visits if the bathrooms are not squeaky clean, and before eating.
