Stockings are indeed a great tradition to maintain. They are sometimes the 1st sign on Christmas morning that Santa has been, when your kid sees that their personalized Santa Stockings has been filled magically over the night. 
There could be stress to spend money on stocking stuff. However, kids are just really happy to have something new during Christmas. You could prevent jealousy and save money by having a budget for each of kid’s stockings.
Make-Believe Toys
You really cannot fit an entire play-set in a sack. However, you could fit several action figures or small kitchen toys. These are great for kids to play on their own and make-believe. You could also provide them a tease for what is to come if there is a bigger playset under the Christmas tree.
Books
Getting kids attracted in reading from an early age has a lot of advantages, from teaching them about empathy to giving them a head start at school. That is why it is best to fill a book into your kids stocking.
Craft and Art Materials
Activity books are good for a little silent entertainment and you can put some new coloring crayon pack too. These would help the writing skills of your kid and maybe keep them entertained on the morning of Christmas. It is also worth filling up some crafty stuff, such as paint brushes or PlayDoh. These are always well-known art materials.
Travel Games and Puzzles
Getting kids to play with family and friends is really fun and it boosts their social skills. Most of these games are funny and keep the conversations going. On the other hand, puzzles are great for playing alone and will develop the logical thinking skills of your kid. This will help them get better at independently finding answers.