This is a nifty little trick.
I like to make my cookies soft, usually, rather than crispy. If you want to keep them soft and chewy (and keep them from going stale), store them in an airtight Tupperware container, and add in there a slice of bread.
The cookies will absorb moisture from the bread (yay, science!) and stay fresh longer. I’d recommend using white bread so that the cookies don’t absorb any unwanted flavors (of course in this picture I only had multigrain so I used that…do as I say not as I do!)
You can replace the bread if it starts to get hard…but if your house is anything like mine the cookies won’t last that long.