When I carry my LCP I generally carry a spare mag in a flashlight pouch in my front pocket with a flashlight clipped to the side. I just tuck the flap inside the pouch and the mag seems to fit perfectly and is reasonably easy to access. That being said, I recently switched to using a couple of single Blue Force Gear Ten Speed pistol mag pouches attached to the Raven Concealment Moduloader Pocket Shield (long names) to carry a glock 19 mag in one and a surefire in the other.
http://raven-concealment-systems1.mybigcommerce.com/moduloader-pocket-shield/
http://raven-concealment-systems1.mybigcommerce.com/moduloader-pocket-shield/