My choice would be the following, Nikonos V with a 35mm lens and Kodak Gold 400
I am assuming that I will be able to get the film processed some day, if I have to process on the island I want Tmax 400.
Why this camera? the Nikonos V with a 35mm lens is a tank and will be good in and out of deep water for a few years then I will get even more years of on land use out of it in any weather. And when the battery dies this camera can still shoot at 1/90 sec.
Why that lens? I know this is not an ideal lens, but it is the best in and out of water compromise lens for the Nikonos.
Why the film? I assume that I would be more chronicling my days, not producing art, Gold 400 will allow me to do that, while the colors will not be all that great, they will be accurate and as they would be more of a document that is what I would want. The 400 film is also fast enough to allow me to get nice bright photos without flash in deep water, late in the day, and when the battery dies in the camera this film will still be able to deliver.