Any bathing suit will do. Bring your own towels as they are not provided on the island. Also, a pair of aqua-shoes would be good as the hot coral is awkwardly shaped and burns the feet (well my sensitive feet at least).
Toiletries and Medical Supplies: Be sure to pack the waterproof UV protectant. Whether you want a tan or not, you need to wear UV protectant as the sun is extremely fierce here in this part of Australia. This lovely lady, was working on her tan, but she had UV protectent with her as I helped her put some on her back. (Lucky me!). Liz of course wasn't too happy.
Photo Equipment: A camera is always a good idea, but be sure to bring a polarizing lens. The glare off the water can ruin what would otherwise be a great picture.
Miscellaneous: If you own it, bring some snorkeling equipment. You will not be sorry.
Luggage and bags:
Pack light - except on food and water!
Clothing/Shoes/Weather Gear: (For summer)
Hmm, bathers, boardshorts and a nice loose shirt - nothing too heavy or you'll over heat.
Sandles are good, but sneakers that are "breathable" - so your feet don't get too sweaty, are good if you go on one of the walks around the national park.
Photo Equipment: Preferably buy film for your camera before getting here, also disposable cameras that you can use under water will come in very handy if you go snorkeling.