I picked up a used Ruger LC Carbine in 45 ACP. Because these are considered "pistols" under Michigan law, they must be registered as such. So, if you have a CPL they can be carried as such! Mags are Glock 21 compatible / interchangeable too. I would have preferred the 10 mm model to backup my model 29 daily carry gun, and truly believe it would be a tremendous option, this one was priced right! It shoots incredibly well. I had to do some careful rework of the SGM 30 round mags to make them reliable though. They are very well constructed and have extremely strong springs, however they had over molded too much polymer in some key areas that needed to be removed.
Whatever's on my hip at the time. Although, I have been known to carry one of my Daniel Defense AR's with a couple extra mags behind the seat of my F-250 SD.