Use them in penny poker games.

I have a Y chromosome and I try to spend change just as I get them, anywhere in the world. Hand over the loose change first then the larger denomination prevents misunderstanding than other way around. I have paid for a 147 jpy drink at a FamilyMart convenience store with 7 1-yen coins and a 1man note. The cashier did not even flinch and happily counted out gosen, rokusen, nanasen, hachisen, kyuusen...

Now, the 10 and 50 yen pieces are useful at train stations and vending machines. The 100 and 500 yen coins are for UFO catchers and other prize machines.