Some airports have collection boxes all around the airport terminal where you can drop your leftover cash before flying out.
If you have currency tucked away in the far recess of your closet from your grand tour of the world 20 years ago, you can exchange them through services like Leftover Currency.
Decorating with foreign coins and banknotes makes for a great conversation piece inside your house and a wonderful reminder of great trips.
If you’ve traveled extensively, you might be able to create the map with coins from the different countries in the map, sort of like a scratch map.
You can also get crafty and DIY by using your leftover foreign coins to make jewelry or glue magnets on the coins to make fridge magnets.
If you have friends who are leaving to travel to a place you’ve been to before, you can share your leftover cash with them as a going away gift. It can help them have cash for incidental purchases right when they land!