Many instructables talk about making keychain out of various material from leather scraps (Leather-Keychain) to more original ones like this cork to dry fishing flies (Fly-Dryer-Floating-Keychain). So basicaly, you can use almost anything for keychain and I had an earring which no longer had a purpose for me.
Did you lost one of your earrings, or they are too old, worn out, or you simple no longer want to wear them? Whatever reason you have, sometimes it's worth to make a small, but cute keychain out of it.
Step 1: Simple Prepare
I don't have a real jewelry tools to work with so I used a simple awl to separate needless part. Also I found unused "cell phone charm strap" (I don't know if it's really called like that), but any metal ring small enough should be good.
Step 2: Separate
No need of special tools here, mostly an awl or big needle is enough. Yet various earrings can be at different sizes and shapes, so this step is for you to decide which part you want to keep and how to do this.
Step 3: Where to Hang It
Here are 2 ideas how to use your earring. One is with a strap, the second only with a small metal ring so it can hang on a zipper.
P.S. Most of earring are small and made of weak material so the best use for such "keychains" is mostly for small makeup bags and purses, not for big outdoor bags. Maybe even the word "keychain" doesn't really fit here, but this is also for you to decide.