Most Cancún packing lists are written by people who've never been to a place where you can buy almost everything you forgot within a 10-minute walk of your hotel. This one focuses on what actually matters.
Sun protection — non-negotiable
SPF 50+ reef-safe sunscreen: Bring enough from home. Mexican pharmacy sunscreen is available but pricier and often lower SPF. Reef-safe is required at most cenotes and many beach areas. Apply before leaving your room.
UV-protection rashguard or swim shirt: More effective than sunscreen for extended water time. Especially worth packing if you're pale-skinned, doing a snorkel tour, or spending 4+ hours on the water.
Quality sunglasses with UV protection: Bring from home. Cheap tourist sunglasses in Cancún offer little actual UV protection.
Clothing — less than you think
Pack 3–4 swimsuits (they need to dry between uses), 2–3 lightweight shirts or dresses, one pair of sandals, one pair of closed-toe shoes if you're doing ruins or jungle activities. Don't overpack for nightlife — smart casual (no athletic wear) is sufficient for anywhere except the most upscale venues.
Electronics
Waterproof phone case or dry bag: Essential. You'll be in and around water for most of the trip.
Portable charger: Long beach and excursion days drain phones quickly.
Power adapter: Mexico uses the same outlets as the U.S. (Type A and B). North Americans don't need adapters. Europeans and Australians do.
Health and medications
After-sun lotion or aloe gel: Burning in Cancún happens fast — even experienced travelers underestimate the UV.
Electrolyte tablets or powder: Heat and swimming dehydrate you faster than you realize. Add one to your water bottle each afternoon.
Your regular medications plus extras: Pharmacies in Cancún are good, but may not stock your specific medication. Bring 3–5 extra days supply.
Stomach medication: Traveler's diarrhea is possible anywhere with different food bacteria. Loperamide or bismuth subsalicylate covers most cases.
What you can easily buy in Cancún
Almost everything available in North American pharmacies and supermarkets: sunscreen, toiletries, medications, swimwear, sandals. Walmart, Chedraui, and Costco all have locations near the Hotel Zone.