Cheap stocking stuffers that are still useful?

Microwave popcorn. Split up a box between all of the stockings.

Socks.

Tape! 2 of my 4 kids have been obsessed with tape in their preschool/early elementary school years. If you've got a tape kid, too, it makes a great, cheap stocking stuffer they will definitely use!

Aquaphor lip balm.

A rolled-up magazine.

Any toiletries, especially those you would buy anyway. New toothbrush, flossers, deodorant, face wash, etc.

An orange in the toe. We always got one growing up.

A paperback book.

Breath mints or gum.

My teen loves the occasional Arizona iced tea, and it's a great cheap stocking stuffer. The can is also giant, so it takes up lots of room in a stocking.

Band-Aids! Huge hit with toddler and preschool age, come in all different character designs, and are actually useful.