If I was stranded on an island like Robinson Crusoe and I had two items to have, they would be a 3-in-one solar panel, battery charger, and lantern. Of course it comes with batteries. The other item would be a taser, for then I could kill small game, and stun larger game that I could then slay with a melee weapon.
The batteries would be very important to charge the taser, and the charger could also provide light, which would be of great way to light up any permanent abode indoors until I could learn how to make candles or some other form of light.
Using the taser, I could probably gain a food source until I could grow and cook my own food. I could go hunting and kill any small birds or other meats which I could then cook on a campfire.