The Situation - Story.
What systems are necessary to live?
Skeletal - The skeletal system is also highly important in this situation. This system contains your main frame, and is what holds you together. Without it, you wouldn't be able to be a real person, per say. You'd just be a large blob of organs and skin. That's not good. This system's main function is to allow you to move and function.
Digestive - The digestive system allows you to get nutrients from any food you can find on the island, such as coconuts and edible plants. Just be careful, because if you eat something your digestive system can't handle (like strange plants, just don't try eating it unless you know its edible, okay?) you're in a bad situation.
Circulatory - The circulatory system is also very important in all situations, including this one. The circulatory system's main function is to deliver oxygen, blood, and nutrients to cells in the body. This is important because it contains the heart, and you can't live without one. Without a heart, your brain wouldn't be able to get the nutrients it needs, and you couldn't function. On the island, you need to be able to work properly, or else you will not survive.
Muscular - The muscular system will help you on the island by helping you lift large objects and will allow you to break into coconuts as well. Though you may get sore, the muscular system won't hurt you in any way, unless you're on the island for four years.
Respiratory - The respiratory system brings in oxygen for cells into the lungs. This is important when you go on long hikes to find food, because you will be breathing hard and getting lots of oxygen. it is absolutely necessary to breath, if you don't breath, you will die.
-So after you know the basics of body systems, as long as you know what to do in a survival situation, you're set.