Coins
Quicky: since you have absolutely no use for ¥1 and ¥5 coins, in regard to paying for things at machines (for instance, ticket machines), it pays (no pun intended) to get rid of these coins when buying stuff at shops.
Kombini (convenience markets) have items that are all strangely priced. That is, nothing is exactly ¥200 or even ¥199. No, an exemplary item will cost you ¥213. Just perfect for getting rid of small change.
But, mind you, when you pay with bank notes or coins of ¥100 or ¥500, you will get even more of these ridiculously inconvenient coins.
Oh how I wish I could just pay for everything and everywhere with my credit card…