How can I use old medicine containers?

You can use them for organizing small items, and here's an idea for a small sewing kit in a bottle: https://www.hometalk.com/diy/organize/storage-ideas/waterproof-sewing-kit-from-a-prescription-medicine-bottle-22893297

Waterproof Sewing Kit From a Prescription Medicine Bottle

Storage for hair and bobby pins, safety pins, straight pins, screws, nails, bolts, paper clips, lapel pins, earrings and twist ties for kitchen. Container for quarters, nickles and dimes. For emergency money fill small containers with assorted paper money rolled , say 15 to 25 dollars, keep in car storage compartment or bottom of purse. Smaller amounts in child's school backpack. Emergency pill box kept in purse with 5 of each pill I take. Large ones I use to give or mail plant cuttings with ends of cuttings wrapped in damp paper towels which are covered in tiny scrap of foil, all tucked in large prescription medicine container. If hiking or camping fill container with dryer lint for fire starter. For eating on the run packages of salt, pepper, sugar, powdered creamer, catsup and mustard stored in car storage compartment.

I've seen people cover them with washi tape or decoupage paper and then use them for storage.

I keep spare pills that I am on and keep them in my purse.