Loads of leftover foreign currency

Contact your nearest airport, they always have a large container for any foreign currencies for charity.

Our local hospital collects foreign currency for charity. Don’t give up on the RNIB . I sent for a box for used postage stamps and it arrived about three months later when I had completely forgotten about it.

I donated mine to the British Legion through Sainsburys, they told me when I got my poppy, and I dropped it in the next time I went shopping there.
www.britishlegion.org.uk/get-involved/ways-to-give/partner-with-us/our-partners/sainsburys

Marks and Spencer has a collection box for foreign coins and notes in their bureau de change near me.

Many charity shops will take them as donations.

If it’s a good few pound gift to someone who is going to that destination for birthday or Christmas treat

These suggestions are interesting to me too, so thank you all. We've got bags all over the house with foreign currencies in, kept thinking we might return but never did.

As Greenfinch suggested, our local hospital takes foreign currency. Not sure what they are collecting for at the moment, but when we donated, it was going towards a Scanner I believe.
So it may be worth asking if you have a local hospital.

The charity Mercy In Action take foreign currency.

We always throw any leftover coins in the charity box as we come through the airport, but we got round to gathering all our bits and pieces of foreign notes recently and took them to a bureau de change. We got 170 Euros for them. It was a nice surprise as I’d assumed that some of them would be out of date, but none were. The only ones DH came back with were our leftover Moroccan dinar - it’s a closed currency apparently.