I like to use real money when learning about currency. The plastic stuff doesn’t have the same impact. But how do you keep your students responsible and make sure that you get everything back? I use this printable, laminated.
At the start of the lesson (in their groups) they lay all their coins on this sheet to check they are all there. Then at the end they lay them all out again, I check it and put the money back in the zip lock bag.