On Friday, November 28, 2014 1:00:58 PM UTC-5, HerHusband wrote:

My first thought is if it's just for a day, whatever min is in
that 80 gallon tank, ie assuming it's almost about to kick the
pump on when power goes out, would be enough for me. Or that
plus a couple of 5 gallon jugs.

One easy option would be to adjust the kick in pressure on your 80
tank so that it doesn't get as low before it kicks on. That should
give you a min of 20 gallons to work with. Or add
that second tank in series, so that it's always full of water, no
air. If power goes out, you'd only have pressurized water for
about as long as you do now. But you could still draw X gallons,
X being the size of the additional tank into buckets. I guess you
could also plumb in a tank of compressed air that you could activate,
that would then provide pressure, so that you could use the full 80
or whatever gallons.

For me, in lieu of all that, I'd just get a generator, because not
only can it supply water, but it can keep the heat, lights, fridge, etc
going too.