To me, it's simple: if you've got the time, use it to get ready. What else could you possibly have to do that's more important? Yes, maybe you'll learn how to do a few things you'll never wind up actually needing to do, but that's a much better problem to have than needing to do something and having no clue where to start.
An Astronaut's Guide to Life on Earth (ed. Little, Brown, 2013) - ISBN: 9780316253048