I remember reading Golding as a schoolboy and his style is not the easiest and this reminds me of struggling with homework. Not sure what I was meant to be learning reading this sort of stuff but as an adult it is still a test of endurance.
The struggle that the survivor has to find food and water and plan a rescue attempt on his rocky outcrop is being written in what feels like real time.
The battle to survive is mixed in with memories fleshing out the characters recent history and background. His drafting into the navy and his pre-war relationship with shipmate Nathaniel is also given more context with the two of them being connected someway, possibly through the acting field that the main character is involved in.