What?

I am girding myself before my deep-dive into the weekend of the long-awaited shed-moving, combined with the weekend of celebrating family birthdays.

We emptied the shed in preparation three weeks ago, half beneath a tarpaulin in the garden and half chaotically indoors. Since then I have Freegled a few things I will never use, but this one perplexes me. How and when did I acquire a Belgian mail sack?