Two magazines: I've been carrying the spare magazine for my M&P40FS in a belt clip, while carrying a standard 40C magazine in a 40C. Two pluses: If I actually need the fool thing, it'll work, and fit, and that's a lot of rounds.... And, if I decide to grab the 40FS for some reason, I've already got a suitable spare magazine on my belt.
(I think I've mentioned this before - I carry an M&P40 - usually the Compact - around the house. Lighter gun than a 1911, and it doesn't require a special belt. Good holster, though, for the 40FS. "Outside", it's an Officer's sized 1911. Heavy, special belt & holster, but tack drivers and dependable. The 1911's also are already set up with night sights and lasers. The budget just won't handle upgrading one of the M&P's at this point.)
On the road, the M&P40C is an "airline travel gun" - I wouldn't get too upset to get an insurance check for it, preferably after I got home, and I have no problem carrying it while I'm wherever. I'd hate to lose it in an uncompensated way, but it doesn't have the blood, sweat, and tears in it as does either of my small 1911's.
Regards,