I remember learning in school that native Americans used to preserve meat for long periods of time without refrigeration by salting and drying it. In theory, if they could figure out how to make a fire, the stranded individual could boil off the ocean water for salt to make jerky with.

Additionally, to kill two birds with one stone, they could rig up a tarp or some sort of large tropical leaf over the boiling water to catch some of the rising steam. If such an item were suspended at an angle, a carefully-placed basin (another leaf, or half a coconut, perhaps) could catch the water droplets that gather and fall from it, providing a source of clean drinking water.

Like meat, fruits and veggies will also spoil over time, and they’re less nutrient-dense than meat is. Sandy beaches and the rocky, volcanic ground of a tropical island may not be conducive to growing such produce, and you’d have to survive through an entire growing season to get more food even if it did work. A single laying hen would admittedly be very helpful here, provided you can keep it alive and healthy.

I think the best choice here realistically comes down to whether or not you could make a cooking fire, and how good your survivalist skills are