This is another super-cheap, simple idea. It's easy to make in a few minutes and can provide a lot of entertainment in "quiet" times.
These are our homemade felt faces. You can make them with just a few pieces of felt (flannel works too but it frays). I cut out ovals in several skin tones and other various shapes from a variety of colors. The boys can make faces, and rearrange them as long as they want. They can even use the felt pieces to make other objects!
What was your favorite quiet activity when you were a child?