I'm definitely in camp coin purse https://www.flyertalk.com/forum/28090605-post8.html Also buy a small 10 x 10" or 12 x 12" washcloth hankie to dry hands with if you will be using restrooms outside of high end department stores & restaurants. You can get both at a 100 yen store or possibly a combini. I tend to hoard 100 and 500 yen coins for coin lockers (now increasingly IC/suica card compatible at city train stations but not always) and business hotel laundry. I periodically try to offload the smaller denominations at the combini (or use IC to reduce small change) or physical suica card recharge machine. Cash comes in handy at small eateries such as ramen/curry tickets from vending machine, street food vendors, temple entrance fees, temple donations, vending machines away from train stations, and small out of the way shops.

Possibly also tuck in a small folded grocery bag for packing your trash with you. Japan started charging for plastic bags at combini, supermarkets, and drugstores https://www.japantimes.co.jp/news/20...c-waste-falls/ You will find trash cans onboard trains for disposing of ekiben containers and bottle recycling stations near vending machines. Any to-go coffee cups will generally be hard to toss once actually away from the shop.