If you even think you might want to do an independent project or a senior thesis, you should pick up materials while you are in Japan. Magazines are a rich source of advertising. Posters of political candidates will support your thesis on the Japanese political system. These are things that are much easier to pick up in Japan than to try to get once you have come back.
You might also pick up exhibition catalogs from museums, clip out articles from newspapers, videotape movies or documentaries.