Since almost all Kindle versions have Audible access, you can turn your old device into an audiobook player for times when you would listen rather than read.
Playing audiobooks requires your Bluetooth connection to always be on. To solve this issue, just connect your old Kindle to a Bluetooth speaker and keep it plugged into an outlet.
You can make a DIY photo frame using a Kindle, wood pieces for a frame, a back cover, wood glue, a hand saw, sandpaper, wood polish, measuring tape, and binder clips.
Start by installing a digital photo frame app from the Appstore, configuring it to display the pictures you want, and placing it inside the wooden frame you built.
An old Kindle can make for a kitchen aid by turning it into a digital cookbook. Just go into the Appstore, search for recipe apps, and install them on the Kindle.