My sister and brother-in-law were having a really tough year, especially financially. On Christmas morning they woke up to extra presents for the ‘kids’ (teenagers), food in the fridge and a bag of coal for their living room fire.
It’s been about 10 years and they still don’t know where it came from, the kids are now adults and still believe it was Father Christmas.
(It’s not a mystery to me, I snook in and did it on Christmas Eve, but I love that’s it’s still not solved)