On the SD cards, almost certainly no effect, that’s one of their selling points. A hard drive is supposed to be sealed with very low humidity air inside it (preferably even inert nitrogen, I’m thinking). While condensation inside the hard drive mechanism is I guess remotely possible, the drive motor’s bearings may be more affected by cold if deeply cold-soaked, then the platters. If you leave the camera int he cold all day and night maybe it could cause a problem, but I think yuor chances are slight. Problems with the lens going from warm and humid, to deep cold and back again, are the most likely problem area. Also LCD screens can be damaged by deep cold. I’d worry more about the LCD and lens than the drive. Keep a hand held hair dryer handy, preferably one that can also run on 12 volts. Use it to help rapidly air-dry (not HEAT) the unit if you ever get into trouble with condensation.
Ironically, cold can be a GOOD thing for some hard drives: When one of mine went bad in my mac, I followed advice on the internet, put the drive in a ziplock bag and kept it in the freezer overnight. I had everything else ready in the mornign to copy files off, , yanked the frozen drive out of the freezer, plugged it in and turned it on. It booted right up as soon as I powered it that next morning, and I was able to transfer off my important files one last time. Just an hour or two of cold won’t “fix” a dead drive, but overnight cold-soaking seems to actually work in this “voodoo method”. Once the drive warms up, it won’t boot again if you power cycle it. But I did the cold start thing three times and by cracky, something I read on the internet is actually TRUE in this case. Go figure.