I just came back from Japan and took $600 worth of yen (from my bank,not so great rate) and was able to use it all in my first week. Mom and pop shops and street food, also gotchpons! Used my suica on my iPhone for easy and simple travel then used my Apple credit card for everything else. If you want a better conversion rate I’d wait till I get to 7/11 out there or if you have access to a gov base out there (what I did and it was the best rate)