Imagine yourself on an island. 

You might be stranded but what is the thing that you need that moment? 

For me it is my phone. 

Now in this day and age if I didn't have my phone I would be shocked. 

Despite the lack of reception, I could either construct a boat to a nearest landmark

Or one could hope that luck has striked and that you can call someone

This island that I could attempt to call someone for that help. 

That is the one thing I need.