some japan protips
Typically getting money ahead of time is a huge pain in the ass and it's easier just to pay as you go while traveling. Depending on your credit card (which you should check before going) you might incur additional charges for on the fly currency conversions, and you might need to let your bank know you'll be out of the country. Assuming you know the fees (if any) and your bank knows you are there and won't turn your credit card off assuming fraud the first time you try to use it - most larger places will accept mastercard and visa. That said, Japan is still largely cash based and most of the ATMs require chip/pin cards so they don't work with US cards. However, some ATMs work with international cards and these are the ones you want to look for. These can be found at:
While cash is king, Suica is a close second. Suica is the universal debit card that you can use for train rides, vending machines, convenience stores, etc. It's managed by JR Train Lines so you have to buy it at the station. The best bet is to buy it at the JR Ticket station at NRT as soon as you arrive in Japan. You can refill it with cash at JR Train stations as well.
GET A SUICA
Having a mobile phone with data is great. There are a couple options that make sense for the traveler to Japan:
You can easily rent a mobile phone at Narita and use that. You can find vendors that rent iphones, android phones and, of course, your japanese style flipphone.
One vendor that has worked well, is G-call. They have a booth in both terminals of Narita and are pretty english friendly.
If you happen to have a Japanese resident who can be your permenant address, you can buy a prepaid mobile phone for pretty cheap. Then you can have a dedicated japanese number and phone. This is helpful for the repeat visitor.
Internet in Japan is not what you would expect.
Free and open access points is very rare in Japan. You can find some telecom owned APs, but usually they require an account or the ability to read Japanese. Quite often, the internet is pay only.
You can occasionally find FON WIFI and sometimes it is free. You should not expect to find free internet while wondering around Tokyo.
Not all hotels have WIFI. In fact, some hotels will bring a WIFI accesspoint to your room and plug it into the ethernet jack to provide WIFI for you in room. Check on foursquare or on tripadvisor to find if a hotel has wifi.
You can easily rent a mobile access point from a vendor at Narita. This is the most surefire way to get internet while traveling in Japan. You can get a very fast and very small AP for around 10 USD a day.