Oahu
Make sure your sunscreen doesn't degrade the beautiful marine life of Hawaii (bereefsafe.com). A single drop of the common ingredient oxybenzone—even in a body of water the size of 6.5 Olympic swimming pools—can damage coral... and over 40 percent of reefs are already contaminated. Brought the wrong kind? Guests at the Surfjack can trade polluting brands for ocean-safe sunscreen.

Hawaii and the mainland limit the flow of agricultural products to prevent invasive pests. But the USDA regulations aren't as cut-and-dried as many visitors fear. For example, seed jewelry and most flower lei are fine, but cactuses and plants in soil don't make the cut.