Always have a ProVari with a Cartotank, and start the day with a fresh battery.
For a long day, I'll bring an extra battery, and when it's feasible, also bring my Reo/Cyclone.
Was just packing for a 12-hours out day tomorrow, and realized, I ALSO, for long days, have a "grab and go emergency" kit - one of those EGO cases that's got about 5mls of juice, a carto-pusher and spare carto, some wick, and room for a backup battery or two.
So if tomorrow, there was a snowstorm and I got buried in an avalanche, I'd still be able to vape for at least 24-30 hours.