Books I have read more than once :
It will be a Classic for future generations : Louis de Bernieres -"Captain Corelli's Mandolin" in my UK edition, called simply "Corelli's Mandolin" in US. (Soon to be a major motion picture coming to a theater near you, or so I hear.)
Jack Finney - "Time and Again."
Arthur Meeker Jr. - "The Ivory Mischief" the prefatory note reads : "None of the characters in this novel is imaginary." Copyright 1941 The Riverside Press Cambridge Mass. It is an historical novel and was my intro to the genre.
When I was young I read "Jane Eyre" several times. Later I came to appreciate "Wuthering Heights" (and better understand all that naughty stuff between Cathy and Heathcliff)
I have three shelves of Hawaiiana which I go to when the Islands call to me : "Ruling Chiefs of Hawaii" is a good one to dip into at random --Von Tempski's "Born in Paradise" is the true story of a young woman growing up in the 1930s -- and for history, dates etc - "The Queen's Story" and "The Betrayal of Liliuokalani" -- and a book of Hawaiian sayings.
Now as to "if you know you are going to be cast away to an island, with no hope of being rescued, which 12 books will you take with you?"
Top of the list would be "A Guide to Practical Shipbuilding."