Santa fills the stocking of younger believers here. My top tip - don’t buy a stocking that is too big, they’re easy to fill when they are little, harder when they are bigger when everything is more expensive!
We always have some chocolate coins and a satsuma in the bottom of them here, then other smallish (often cheap) gifts to fill them out. It could be sweets they’re not normally allowed, mini cereal box that is more of a treat, lego blind bags, book, stationery, hair clips, socks, pants, card game, rubies cube, mini puzzle, bath bomb, toiletries, spare phone cables, mini puzzles, puzzle books - all depending on age.
Stockings used to get left on the bed to be filled by Santa, but that got too nerve wracking, so it moved to the bedroom door handle. Some people have two identical stockings so they can quickly swap out the empty stocking with the full one.
DC always brought stockings into our bedroom to empty out the contents before going to see what Santa has left under the tree.
We do stockings for adults in our house too, because we think it’s fun.
There are lots of different traditions in the UK. Some people find ‘Santa’ very much an American import and stick to Father Christmas, but in Scotland (where I’m from anyway) and other parts of the UK it has been Santa for as long as people can remember.
IME of living in different parts of the UK, it is more common in England to have Father Christmas fill stockings, while parents leave presents under the tree. It’s not universally the same though.
I was brought up with Santa bringing everything except presents from other family members (though my grandparents used to arrive with gifts and say Santa left them at their house for us), so that’s what I’ve always done. DH was the same, but we both come from central Scotland.