Particularly indispensable for travel to dive coral reefs are two pieces of accessory equipment. First, you should bring along a sturdy, good quality gear bag large enough to hold everything you will want on the dive boat. This will enable you to conveniently keep all your gear in one place during travel, and provide a safe place to store your dry clothing, towels, sunglasses, etc. while in the water.
Second, bring along a quality pair of polarized sunglasses, with dark lenses designed for the brightest conditions and plastic or nylon sport frames that can take some rough use. At sea or on land in the tropics, quality eyewear is essential for good vision, and polarization allows you to see the water colors of varying depths as well as reefs as you approach dive sites.