You could also do a fanfic where instead of the boys being from a civilized society, they are from a more primitive or war - torn society to begin with. This would affect how they view the island and the rules they create. Maybe they would be more used to chaos and violence, or perhaps they would have a stronger sense of community because of their difficult past.
Another idea is to set the fanfic in a modern - day version of the island. The boys could have access to some modern technology like a broken cell phone that they try to fix to call for help. This would add a new twist to the story as they deal with the same basic problems of survival but also with the allure and complications of technology.