The coldest that I've had my camera in was a particularly windy glacier in Iceland. Very, very cold with the wind-chill (maybe -15 to -20 F). Went from that to a slightly warmer bus to a much warmer hotel. Didn't take any precautions - also didn't notice any condensation nor fogging.
What I've come to learn is that cameras are pretty darn tough and resilient.
Second example: My wedding photographer shot our wedding in Portland, Oregon, in March while there was snow on the ground (and indeed, more snow falling!). He went from out in that and back to inside shots without worry and I didn't notice any condensation or fogging on his equipment. Resulting shots didn't appear to be shot through a fogged lens either.
I'd love to see a study of what humidity levels and temperatures are needed to really cause problems for shooters...but until then, you've got just a few options:
Option A: Wait for the problem to present itself. Simply go about your normal shooting and, if you notice condensation or fogging problems, then look to solve.
Option B: Solve the problem before it occurs. Obviously, the absolute best thing would be to have an airtight bag with silica gel inside that you wrap your camera in while in cold areas and before bringing into warm. Outside of that, having some silica in your backpack and simply leaving it closed until things warmed up may not be too bad. But, if you need to shoot immediately inside...all bets are off, start shooting and prepare to wipe fog off the front lens element and pray it doesn't fog up inside the lens ;-).
All that being said, in my own experience...condensation issues are like the uv filter vs lens hood issues...everyone's got a reason to go one way or the other, and hardly any of us end up breaking the camera/lens anyway.