oh I can't! The question is so helpful though. It makes me realise that I mainly read to learn and enable me to communicate better and write better and be kinder. On a desert island all alone I would be reading purely to enjoy the time. I should give more thought to this. There are very few books I want to read again once I have read them; that would be a big issue

Drawing on the Right Side of the Brain would probably be a good one... I would spend a lot of time drawing (assuming I could make some charcoal and parchment or whatever) and I need help to get started! On the other hand, practice makes perfect...
Is there a complete works of Jorge Luis Borges? I think his musings would inspire me to muse mathematically.
I have a book Fifty Women Poets on my tbr pile and it's quite fat. I'd probably grab that if I knew I were about to be marooned; hopefully it would yield much for reflection...