Hey, a lot of people are going to Japan or posting about going to Japan. I just returned from my second backpacking trip, so if you haven't been before, here are a couple of tips.
Bring:
A hand towel - most Japanese bathrooms don't provide paper towels or dryers, so most Japanese people carry around small towels. Also handy for dabbing sweat if you go in the summer.
A sleeping mask - are you staying in a ryoken? If so, do you like having gentle sunlight coming through shoji screens waking you up at 6 am? I don't. If you don't either bring one.
A phrase book - most Japanese people will speak enough english to help you and you'll be able to point your way through most transactions. HOWEVER, if you at least try it's much appreciated. You really won't need to know much, but a few key phrases will make you seem like way less of an ass.
Gold bond - I'm serious. Especially if you go in the summer. It's very humid. It'll help you not chafe.
Don't bring:
Converters - they have the same plugs we do.
Any "just in case medications" - just find a ¥100 shop and buy what you need there if you need it.
Tissues/wipes/etc - some people always travel with these, but don't bother, they hand out free packs of tissues in subway and train stations and you get a wet nap every time you buy food.
Too many clothes/undies - laundry service/laundromats are available everywhere. Just wash your stuff when you're running low.
An umbrella - yes Japan is rainy, but just buy a ¥500 yen umbrella from a convenience store if you really must have one. Most hotels and ryokens will have ones you can borrow for free.
My last tip: Japanese beds are really firm. If you ABSOLUTELY NEED a soft bed in order to sleep, I honestly recommend you bring a thermarest if you're backpacking. Ryokens will provide you with a futon on a tatami mat, and the salaryman hotels seems to choose the mattresses that will best replicate that experience.
¯\_(ツ)_/¯

* Get bright lights in your eyes if you start to feel sleepy.
Konbinis are everywhere... as in even I'm in a low-populated area of suburban, far-away Nagasaki and even here there are 3 different konbinis AND a Don Quijote department store (like a konbini but on steroids) within 5 minutes.

One important tip on plugs here, btw. Wall plugs are the same voltage but generally do NOT have the third grounding plug which you would generally be required to use for plugging in your laptop and a few other things. You can buy a converter for 100 yen + tax at any Daiso, Can-Do, Seria or other 100 yen store.

Bryce Pugh

Leslie St. John Cameron Campo Maria Isabel check this out

I don't recall soap or TP in the bathrooms either; has that changed in the last few years?

Jess Sung

Sara Reid

If you're visiting Japan I'd also recommend pocket wifi & the google translate app, you can draw in characters for translation, so helpful!

I never saw a bathroom without soap and TP. For the person who said they all have hand driers. In Tokyo/Osaka city type places yes. In small rural train stations and parks, no. I didn't see a single bathroom with a hand dryer or towels in all of Nara Koen.

If you find pocket wifi too expensive, you can also get a sim card just for internet access and then just use your phone as a hotspot so other people in your traveling party can use the internet as well. Cheapest pocket wifi and rental simcard I found was from here: http://rental.cdjapan.co.jp/ it worked like a charm except for the last few days of our trip when it was slower than usual.
RENTAL.CDJAPAN.CO.JP
CDJapan Rental Best Rate Rental Sim Card & Mobile Wifi Service in Japan

Thanks for taking the time to post this! I'm heading there in Nov.
Working on the phrase book now. Surprised they use the same plugs we do.

The voltage on the plugs is lower - 100v instead of 120v like we have here, but I didn't have any trouble charging my phone, camera battery or 3DS. I know Apple bricks just do the converting for you.

Is airbnb a good/cheap option for staying in Tokyo? I don't mind being a 30-60min train outside of the central area.

airbnb is great. Depending on what you want from your accomodations, you may not need to stay that far out.

how about using Debit card for withdrawal of yen is it easy?

Finding bank machines can be tricky. There are lots of them, but your average Japanese bank machine won't work with your card. Your best bet is to find a post office or a 7-11. Both of the bank machines in those places will work.

I am stopping in Tokyo for 2 days my way to Hong Kong any suggestions what to see and do in Tokyo , staying near Tokyo Station