If you only had a pocket full then I'd say take the bus more often or use them for dinner tonight (they might get made for having to take 20 rmb in coins, but stick to your guns and they'll take it).

But since you have boxes and boxes.... I say save them up some more and find a kiddie pool. Then enjoy an afternoon Scrooge McDuck style Then you can start having food and crates of beer delivered to your place and pay them in coins still you're only left with the kiddie pool.

Then with all the food and beer you have sitting around your place, throw nice little party and use the pool as either a hangout place (if it's hot) or as a way to introduce a few local girls to the Western culture of oil wrestling.

give them all to a really in need homeless person , such as someone visably disabled

I save them till, a new years time frame or a summer time frame, take them to your local xiao mai bu( street corner shops) and they will change it out for you, and believe me kuai and mao add up!!!!

If they have pandas on them, send them to me

Take them to the bank.

Slowly start using them. You may have a lot, but if you use them little by little, one day they will be all gone. Why didn't you just use them in the first place?

Most small shops or covenience stores will be happy to take them and give you bills in exchange.

Well you've already counted the money as gone (as far as you daily habit of not making sure the spend said coins). So I say just throw the box of coins away.

Hear me out, there are so many fake beggars out there that it is hard to tell who could actually use the money. But most would agree that those individuals that dig through the trash to collect any cardboard or plastic thrown away really could use the money. So throw the box away and when some poor guy is digging around in the trash and finds a box of money, it will make his day (life).