My top tip with stockings is not to buy too much too early. I'm very disciplined when it comes to main/ family presents but I get a serious case of The Twitch when it comes to stockings. I keep a list on my phone so that I can write things down when I get a good idea.
Also, keep each item down to no more than £5, otherwise it's not really a stocking present.
My two (dd - 6 and ds - 2) will usually get a net of chocolate coins and a satsuma as well as a chocolate snowman or Santa (and last year, because I twitched, a pack of Haribo Minions......)
They both also get socks and this year - for the first time - they'll BOTH get pants (starting to potty train DS).
There'll be some kind of novelty toiletry for them both - Thomas the Tank engine bubble bath and Frozen shampoo last year.
They'll also both get a book - I'm planning on getting Matilda by Roald Dahl for DD this year. DS will get a colouring book and DD will get a book of puzzles.
Last year I knit them both an animal hat - DS had a lion and DD a rabbit. I'm thinking bedsocks for DD this year and mittens for DS, but we'll see if I have time.
They're also both getting swimming goggles this year - DD's have broken and DS will be getting his first pair.
And once I've got all those, I'll keep an eye out for some fun toys and other things they'll like. Frozen Top Trumps were a huge hit with DD last year - just something that caught my eye at the checkout. I don't want the stocking to be so full of 'planned' gifts that I don't have space or money to buy some whimsical last minute things.