Great poster, my only comment would be that a spare mag is more secure shoved under the belt halfway inside the pants, than loose in a cargo pocket. But that's a tiny point.
On that line, here's a cool tip. If you duplex your mags, you have two ready to go side by side in your rlfle. Then your "grab and go" spare is a second duplex, which you shove upside down, one mag inside and one mag outside of your pants.
Very secure, very fast, and you have 4 full mags loaded and on your person, without jocking up with web belts, vests etc.