Sunscreen is destroying coral reefs. Make sure to apply an ocean friendly sunscreen before you dive into the ocean.

In the islands, fresh water is a limited resource. If at all possible, please conserve water.

If you're visiting someone's home, remove your shoes at the door. Respect the culture of the land you're visiting.

Do not, and I say DO NOT, take any rocks from the island home. Hawaiians believe those rocks and gravels to be sacred. Once again, respect the culture of the land you're visiting. It's said if you take back those rocks horrible things are bound to happen.

Place any beverage container on top of or immediately adjacent to the trash receptacle after discarding it. This is courteous—beverage containers can be redeemed for 5 cents each, providing a tiny source of revenue for anyone willing to rummage through the trash. Don't make them rummage through the garbage.

Keep valuables out of your rental cars. And, if necessary, keep your valuables in a safe place before arriving at your location.

Hawaii's posted speed restrictions are far lower than those on the mainland. Much lower, in fact. Don't go too fast, and drive defensively. Be aware that most roads run along the edge of cliffs or beaches.