Cannon's Powershot SD line is a great light compact camera that takes good quality video to capture the great moments on your vacation.
You can carry all of your essential daily needs in a backpack while on vacation. It folds down to a compact size and is lightweight to fit into your luggage.
It's always great to go snorkeling in Hawaii any time you want without renting the gear that someone else used! There are plenty of free snorkeling on all of the islands.
Bring an empty duffel bag with you in your luggage and fill it with the items that you purchased on the islands for the trip back home. Duffel bags are relatively inexpensie and are lightweight.
Sunscreen is a essential item on your Hawaii vacation. The sun is intense and while it may feel good, many people get severe sun burn. If you have fair skin, you should apply a minimum of SPF 30.