It kind of depends on what you want to do. As I've been using my 35mm mostly for bird photography for the last few years, I would have to say the 400/4.5 and 600/4.5 are my normal lenses and I'll often bring a 90/2.5 macro for the occasional macro along the way, but that's a fairly esoteric set of choices.

And bird photography would be the thing to do on a desert island, after all, since the birds come and go, and there would be a fair amount of variety, while landscapes and self-portraits might get a little tiring after a few years, and street photography just wouldn't make sense. The 90 macro would be fine for still lifes, and I guess since I would have lots of time on a desert island, I guess I could composite some big panoramas with it, so I wouldn't need a wide lens.