Mark Johnson, Via the Internet
A) Just put it in your right pocket, your right pocket, your right pocket, you’re getting sleepy…
Kidding aside, I feel your pain. Developing a lens cap habit can be difficult. If you shoot wearing the same type of clothes and in the same type of temperature conditions, it can be fairly easy to say, “I’ll put it in my shirt pocket.” But if you shoot outdoors in the winter, your shirt pocket isn’t that accessible. The recommendation I have is to try to make a conscious decision, before you go out shooting, where you’ll put the lens cap. You might even have to say it quietly to yourself a few times when you first start shooting.
While they work well for some people, I’m not a fan of lens cap keepers. I don’t like something hanging from my lens that may induce vibrations.
One other comment about where you put your lens cap: Think about how clean that pocket is! Every time you put your lens cap in your pocket, you’re loading it up with any dirt, dust or lint in your pocket. When you put the cap on the lens, you may transfer all that junk to the lens surface.