http://www.lovehoney.co.uk/product.cfm?p=35261 King cock nine inch dildo and harness. Assuming I'm stranded there with my wife she can peg me and I can use it on her as well for further fun.
This is a tough one, My desert island toy would be my Lelo smart wand. If no power then my icicles 14 glass dildo (made for anal but perfect for g-spot stimulation xx