Seriously I think the biggest rookie mistake of all travelers is OVERPACKING. I walked into my friend's house and it appeared that he was packing his entire house. He was planning to bring 3 full sized luggage for a 2 week vacation. I helped him narrow that down to 1 bag and only had him overpack socks and medicine. Since Japan is a industrialized nation they do have pretty much have everything as in the US. If you are more of a tourist, I'd also pack a small (empty) duffel for gifts or souviners. There isn't anything worse than buying a bunch of stuff and having to leave it when you realize you don't have space...(as what happened to another buddy 2 weeks ago)