Have you ever heard of a Magic Slate?
It's a toy that you can use to make marks which can be "erased" by separating the top layer of plastic from a bottom layer of darker permanent pigment.
The material is mounted on a decorative card which can be removed for a more formal appearance. Although it comes with a plastic or wooden stylus, you can use anything to make a mark such as your fingernail. It's reusable. Permanent copies can be made on a copier or with a cellphone camera before the content is lost.
If the size of the active area is too large, it can be cut easily with shears or an art knife or even a paper cutter.
When you're bored, you can use it to doodle. The marks appear dark on a light background.
As far a tech goes, it's about as low as you can go and as cheap a solution as you'll find.