When I was a kid, my mom and dad always put an apple and an orange in the bottom of my stocking.
Besides a lot of what’s been mentioned already, everyone in our family gets a very small Lego set in his or her stocking, no matter your age. Kids to adults, you get Legos. It’s a silly thing we all look forward to, started by my mother-in-law when her kids were little.
How about a small blank book or journal with a nice pen? Some fun markers or arts and crafts supplies, silly refrigerator magnets for adults, fun holiday socks, homemade candies or treats, or novelty gifts. I once found a set of pens at a bookstore. They were designed to prevent people taking your pens and looked like pens from businesses except they said things like Sex Addicts Anonymous instead of the name of a bank or normal company. We put nippers (little bottles of alcohol) in my father-in-law’s stocking.
You could start your own tradition of putting a unique Christmas tree ornament in each stocking, with the person’s name and the date written on it in permanent marker. We started doing this for our kids’ stockings years ago, and now when we decorate the tree they love to find their own ornaments and remember past Christmases. Someday when they move out, get married, and have their own families, they’ll each have a good set of ornaments to start out with!