A fishing rod to catch fish with so I could eat, there would be plenty of drinking coconuts on the island so a good Swiss Army knife with all the tools in working order would be a must, and a lifetime supply of matches to light fires.
I want to say a blanket and pillow too, but if it's only three things then I'd have to work out how to make these because they are luxuries and not necessary to survival.
With the earth being ravaged by us, we may find ourselves with more dire questions than this. As a first step, I and my wife have been trying to live with minimum things..
That apart if faced with such a question - I'd beg to take my wife along because with her by my side I can face anything..
Next for the 3 things:
(1) survival kit - whatever I've observed being used by bear grylls
(2) sources of water and fire
(3) the knowledge and the ability to wake myself out of this nightmare so I can return to my day job!