Sounds like you have some great ideas already and stockings that are amply stuffed! Does your son like beef jerky? That might be a nice edible treat to add if he likes it. Maybe a favorite magazine rolled up and tied with ribbon? Your local NAPA store might offer some great ideas. They usually have small tool kits or maybe you could buy individual tools, a wrench, screwdriver. Maybe the small sizes for working on computers? Little flashlight.
For daughter, I know I can always use nice nail file/emory board. Walmart used to carry a really nice one that has like a fiberboard filler and it measured about 7" long and about an inch wide and the emory part was black. It is my most favorite type of nail file. Rougher on one side.