This is so ADVICE from past and current JET's in Oita prefecture. Please remember, everyone is different and this advice may or may not apply to you. You'll also see that some of the advice will contradict the 'Leave' recommendations
Electric toothbrush heads
Razors in bulk from Costco *Costco is also in Japan although it involves a sizeable road trip
Make up in your colour
Sanitary stuff if you're a woman.
All makeup if you are ghost white. No ghost white foundation exists here.
External hard-drive with music or movies, pictures of friends and family
Ebook reader or tablet,
Anything you need for a hobby that makes you happy (that you can't get in Japan)
A laptop (get a laptop),
If any of your electronics have three-pronged or polarized plugs (meaning one of the prongs is slightly wider than the other) then get an adapter. You can safely use American electronics with Japanese outlets since there is not a significant difference in voltage, so it is just a question of making sure the plugs fit.
GET THE LINE APP NOW BEFORE YOU COME.
Rain jacket and rain boots. Unless you buy them here.
Clothing for both a hot and cold climate
Bras (A shit ton of bras if you are over a US C cup)
Three-five sets of versatile tops and bottoms, a suit
Clothing for hot and humid weather. Cold weather clothing can be bought or sent later.
Winter clothing: expensive to buy here.
Pyjamas you aren't afraid to let students see you in, because they will if you are high school,.