One the most unusual, but rather entertaining ways to kill time is to go to the Oedo Onsen (hot springs) theme park which is open from 11AM to 8AM the next day: http://www.ooedoonsen.jp/higaeri/english/index.html

If you're gonna kill time, why not take a nice bath and sleep on a tatami mat while waiting for the first train to HND?


And I do highly recommend the 24 hr internet/manga cafe just right across the Keikyuu Kamata Sta.
http://www.mangaland.co.jp/store.html?storeid=38