Take a bottlecap and punch two holes in it with the hammer and screwdriver.
The holes don't have to be perfect. You'll cover them later with decorations.
Using the needle and thread, attach the bottlecap to the hairclip.
Turn it over and use the glue gun to attach the bottlecap to the clip a little better. It will just give it some extra safety so it will be more sturdy and not break as easily.
Add your decorations on the inside. You can decoupage it with Mod Podge and cute sequins and glitter and bits from magazines if you'd like, or you can hot-glue tiny pieces of felt in there, like I did.