To go very deep (maybe more than your question intended). I am going to assume that I am stranded on an island with only one food available. I would have to go with something high in calcium to keep bones strong as I aged on the deserted island,, but with lots of vitamins (esp. vitamin C) to help my body fight those pesky tropical diseases that the inevitable mosquitos and wet rainy season may bring about. And, of course it would have to have good levels of protein (to keep me full enough to enjoy those deserted beaches without having to break constantly to gather food), and fiber for those bathroom visits behind the trees. Aha, broccoli, of course.
Of course, this could be just a fun question requiring a simple answer. In that case, gimme chocolate: yummy, creamy milk chocolate and lots of it!