Japan - What should I pack? What do I need to know?

I get a lot of questions about what to pack and specific information about the culture for first-timers to Japan. Japan was always number one on my list of international travel and in 2009 I was lucky enough to go there for the first time. Since then, I have been a couple more times, exploring the culture I love so much more and more. I still have not been to so many places on the island and intend to go there more in the future. I am definitely not an expert in this category