Medicine cabinets are a great place to store all the various bottles, tubes, boxes and packs one needs in a bathroom. They're also small and cramped. Lifehack.org suggests saving some space by attaching magnets or adhesive hooks to the inside of the door and hanging some of your items on them.
You can buy small magnets or mounting hooks for only a few dollars. A small investment that can obviate the need to buy a larger shelf or cabinet for a bathroom short on space. Don't forget you can find some free magnets inside your shower curtain liner, too (or an old hard drive).
How To Increase Medicine Cabinet Space [Lifehack]