Love stocking stuffers!!!!
I don't like filling them with just "filler," so try to go for quality over quantity - having small stockings helps.
I also try to find things that they "need" for their activities/hobbies.
For examply, DS12 is a scout and swims, so might get new goggles (he likes $$$ ones), some new gadget for his first aid kit (last year it was a snake bite kit), bear bell, good water bottle, water proof box, small $ gift card for places he likes, movie gift card (last year I gave everyone a card with enough $ on it to take the whole family to a matinee), fun socks, little
lego sets, drawing supplies, a book, axe body stuff.
DS5 might get art supplies, a couple of dollar bills, little lego sets, funny socks, new goggles, small nerf gun to shoot his brother with, fun bath stuff, a book, puzzle, small game, sidewalk chalk.
DH is a little harder, I tend to do phone accessories and little electronic gadgets, multi-tools, small $ gift cards for places he eats lunch, funny t-shirts, bath puff.
Everyone also gets a toothbrush in their stocking and some snacks/candy that they like that I don't normally buy.