A pen - obvious? Well not necessarily. You could be using a typewriter, a laptop, a chisel... whater your method, there is nothing like a nice, portable pen for taking notes on the go, which, once you start doing, you will begin to get a constant flow of ideas, hopefully.
A notebook. Use one. Don't let yourself get bogged down by having many different notebooks for poetry, stories, your novel, placenames, interesting new words... just one hardy notebook. You can get nice ones that have dividers in if you're so inclined. It doesn't have to be fancy. Keep it simple, but for the love of caffeine make sure its durable and small enough to throw in your bag, because it is your new body part. Yes, take it everywhere, because the one day you leave it at home, will be the one day you have a wonderful idea. It happened to J.K. Rowling. She planned Harry Potter and the Philosopher's Stone on a napkin.
A folder. Look, you will want to at some point, but trust me when I say, NEVER THROW ANYTHING AWAY! Put every loose page, every quote, paragraph and doodle into this folder. You'll be glad you did. Put your Author's Profile in here.
And that's it. That and your imagination. That's all you need. Forget about fancy pens and netbooks and a vintage typewriter. All you really need in the worse case scenario, is a napkin and an eyeliner pencil.
That said, you may now see my unnecessarily beautiful desk.