Some nice tips there Gato appareciated, I am currently swapping over the dedicated M4 pouches to the other side and putting the SAW pouch on the rightside.
I saw the pistol holster mounted in many similar ways on U.S invasion troops and I liked it (agreed Gato it was rare to have one). I play in lots of built up areas when airsofting and I find a pistol is invaluable. Soldiers (MP's especially) found them particularly handy if manning roadblocks, doing snatch and grabs, handling insurgent prisoners. I know it was rare for soldiers to have M9's but they were issued for particular duties.
Regarding Matt Damon, his whole squad in the film are played by Iraq war veterans. They're the ones who are kitted him out and Richard "Monty" Gonzales, the actual soldier that Matt's character is loosely based on, was on set as an advisor and kitted Matt out in the actual configuration he used in the invasion.