You'll often find me hiking in temperatures of -20 and even colder when I visit friends in Alberta.
And I just use the same rules as Duplo. With 1 exception.
I just use a camera bag instead of the ziplock.
I've never had a problem
I should mention that if your going for even the shortest walk bring along a bottle of water stored close to your body for warmth.
And something like granola bars or trail mix.
At least I find that I need more food and water than I do on even the hottest days.
If you don't mind me asking, where are you from Mikhail?