Honey, I traveled around Japan for 3 weeks with one, carry-on sized suitcase- and I was making professional presentations, so needed suit jackets, etc. You're way overpacking. It will be warm- some shorts, a few pairs of jeans or long pants, a few shirts or tops, sandals that you can walk a lot in, something you can sleep in, some underwear. Keep in mind that if you try to check two bags coming back, the airline is going to charge you. The last time I looked into that, it was going to cost me $100. Japanese candy is not worth that! You can get it at any international market in the US.