| I grew up in Minnesota. My first band and bar gigs were with my parents when I was 13. Haven't lived there in some time but there are practical things to do to take care of your equipment in cold weather.
We had a campershell on the back of the truck but obviously your stuff would be freezing by the time you got to the gig. Arriving with enough time to let things acclimate is important.
We'd arrive, take in instruments, open up the cases and let them lay there while we hauled in the rest of the stuff. Speakers, amps, etc., take them in, set them where they're going to be and leave them alone while you go back to the instruments that have had a chance to warm up some and hook them up, tune them etc.
Then go back to the rest of the equipement that has now had a chance to warm up some, wire it all up, turn it on but leave all volumes down and don't use it yet, let it idle and warm up some more while you go back to the instruments that are now closer to normal temp. and retune, etc.
Then go back to the rest of the equipement, turn up volumes, make sure everything works, do sound check, etc. Then leave it all again as if you where taking a break, leave most things up, just turn down instrument volumes before you put it on the stand, turn down master slider on mixer, etc.
Go get something to drink, use the restroom, say hi to bartender, waitress, boss, etc. (not nessecarily in that order), then check tuning, start gig.
Bill's points are spot on in that, it not really the getting cold or even freezing that does the damage, it's the warming up when the frost turns to water. Actually, staying cold for a long time and warming up once may produce less stress on stuff. Corrosion on amp parts, speaker cones getting moist, then dry again. An extreme example is if you've ever seen a piece of cardboard get rained on and then dry out, it ain't quite the same as when it was new.
A good once-a-year/seasonal cleaning with a vacuum and some de-oxit as well as letting speakers warm up before asking them to perform are important. Usually get pretty good and adjusting/setting up instruments in the spring and fall as well, that is if you sort of "live with the elements" and not always in central a/c and heat and all your gigs are 20min. away or less. | 
