[Accessible Japan]

Hello

You may just want to start with 10,000 yen bills as you can buy even small items with large bills here (ie you can buy a $2 item with a $100 bill without much of an issue).

But just in case, get some 5,000 yen bills as well.

Train tickets in Tokyo range from 160 yen to 1,000+ yen

As you use the bills you will naturally get change.