Aloha!
Well, there are somethings that you can't do without if you are planning a trip to any of the scenic Hawaiian islands. This list of essentials shall definitely come in handy.
1. Sunscreen, sunscreen & lots more sunscreen. At least SPF 50 - lotion, spray, gel- whatever you like.
2. Aloe gel - to apply on sunburns or rashes. It cools skin really well. Easily available at pharmacies in the US or buy it in Hawaii.
3. Flip-flops/Slippers/waterproof floaters
4. Sport Shoes - for those beautiful hiking/biking escapades
5. Camera- Well don't forget to carry your camera charger as you might get so absorbed soaking your lens in the beauty that soon you may face the unthinkable - running out of battery. I dread the thought of it.
Take this tip seriously or else you'll find yourself exclaiming, "This can't happen to me!"
6. Sweatshirt/Jacket - Especially if you are planning to view the heavenly sunrise from Haleakala - Maui
7. Hat or cap
8. Sporty sunglasses for Beach Volleyball, pool games and just about anytime on the beach
9. Flashlight - For Haleakala Sunrise - Maui, Moonwalk (discovering volcanoes) - Big Island
10. Cool cotton clothing & beachwear/swimwear
11. Light rain jacket - Especially if you are planning to visit any rain-forests in Hawaii or plan to take the famous drive Road To Hana - Maui.
Explore & have fun!