My first payphone, Merk Tischmünzer 55

[19and41]

Excellent work!  I still have a bag of change I'd saved while stationed near Hameln.  I didn't know the Euro had converted them to antiques over the years.

[countryman]

Deutsche Mark change is antique but still convertible. You can take it to a (national) central bank office and get 0.51 € for 1 DM. The exact rate is 1.95583.
I have been told if you walk in with one single 1 Pfennig coin you`ll get 1 Cent for it, a nearly 100% profit! :-)
On some occasions dealers still advertise that they will accept DM cash as a promotion. Guess they won't take 1 Pfennig though.
An astonishing amount of cash that was issued over the years has not been converted yet. It's sitting in bags and boxes like yours, or is lost, buried, burnt... no one knows.

If you want to get rid of foreign change (with a value >0) there may be charity organizations interested in it.

A Happy new year 2021 to everyone!