I find that wearing a yellow plastic bowl on my head whilst shoving a couple of lit Rothmans up me nostrils works a treat. I only exhale the smoke via my mouth and I feel ok.
A bit of advice from an old un.... Stockpile pencils!
I have over 36,000 of them. In an emergency you can boil down the lead (nutritious soup) and set fire to the wood to keep warm.