While certainly not "on patrol" my duties as a naval officer in the amphibious forces required me to frequently go ashore in Beirut, Lebanon during the unpleasantness there in the early 80's, and move about the city. My normal procedure was to go to the ship's armory and draw a 1911A1 and ammunition, which was already in magazines, 5 rounds per. You got two magazines, for a total of 10 rounds.
When I asked for two additional magazines, the gunner's mate asked me "Why do you want all of those extra rounds, sir?" Mind you, this was shortly after the Marine barracks bombing.
I would take the weapon and return to my stateroom and top off all of the magazines with my own stash, and insert a loaded, personally owned, commercial Colt magazine into the pistol when I got ashore. I rarely trusted the "built-by-the-lowest-bidder" mags that were issued.
We were not allowed to have loaded weapons at the time, because that sent "the wrong message" to the Lebs. This led to me being constantly corrected by Marines and Seabees. ("You don't have a round up the spout of that thing, do you, sir?". "Gosh, Gunny, I didn't realize...etc."). So I had to play games with the system, as it were. At one point, when I didn't like the moves I was seeing, and the looks we were getting from some locals, I stepped across the street from our vehicle and under an overpass, where I was protected from above and behind and could watch traffic on in the street and in the buildings across from me. I had to take my pistol and load it behind my back, to keep my companions (including my CO) from becoming needlessly troubled.
Anyway, had there been trouble, I don't think I would have been terribly concerned about retrieving spent magazines. After 36 rounds of .45 ACP it would have been over or I would have been scrambling to pick up one of the M-16's (or optimistically AKs) lying on the ground.