If you are lucky to have the opportunity to stay at a Japanese home, it is a good idea to bring gifts for your hosts to show your appreciation. Gifts from your country or your hometown go over big in Japan. They do not have to be big or expensive; just something which represents your country/hometown and shows you thought about them and appreciate their hospitality.
Photos go over well too and bringing photos of your hometown, family, friends, work/school is a great idea. Photos go a long way to help describe your life in your hometown, especially if there is a language barrier between you and your Japanese hosts.