Intro: Xiaomi Yi Lens Cap
Quick back story on the camera if you don't have one but are interested. They're a great cheap alternative to a gopro or standard action camera. They use a 16mp Sony Exmor sensor with a great lens and shoot 1080 60p video for about 90$ depending on where you buy them and what color you get. They generally come direct from China but they're available through amazon now.
The problem I encountered is I use this on my quadcopter and I usually throw everything that fits into my backpack. This does not come with a lens cap and its an extreme wide angle lens so the element is a big bubble. So from the junk I had around me I came up with a quick and dirty lens cap. Enjoy
Step 1: Materials
Very simple materials:
Bottle top ( I used a random Mt. Dew bottle top I found)
Rubber Band ( needs to be big enough to go around the camera)
Napkin or Rag piece
Step 2: Cut It
Cut a chunk of your material and stuff it into the cap.
Step 3: Tape It
Tape the rubber band to the cap.
Step 4: Win It
You're set. Super simple and super effective.