I really want one of those tree-burials. I'm not sure if they'll be a thing by the time I die but that'd be cool.
They like put your body into a little pod, and put a sapling over it. They bury you with the tree above you and the nutrients from your body feed the tree.
Otherwise, cremation. If I've published a book by then, burn a copy with me and scatter the ashes about in really pretty places across the world. Donate the organs and then burn the rest. Even though I'd be dead at that point something bugs me about the idea of giving my entire body away for science. Though hand transplants are apparently a thing now? I hope I don't die young, but if I do, well, give those hands to someone that will care for 'em, I guess.