• Three metal five gallon gasoline containers treated with Sta-bil and a manila tag giving me the expiration date based on when it was treated.
• Between 10-15 gallons -- I rotate through, using the oldest gas cans to refill my mower and snowthrower. If a gas can approaches its expiration date before being cycled through this way, I pour it into one of our cars.
• The main use case is for running a generator during a power outage, with a secondary use case being for our vehicles if we have concerns about gas stations being open.
• Not a lot more -- I can get to 15 gallons plus fill up the mower, snowthrower, two small generators, so topping out at about 25 gallons outside of the cars. I also have a siphon for moving fuel from where it is to where it needs to be.

The plastic cans I'd been using started failing and ended up getting replaced.

I no longer have anything that uses fuel-oil mix other than a unserviceable chainsaw I bought super cheap at a garage sale and have never fixed. I've never had an event here where I would have chosen a chainsaw over my two saber saws (one corded, one cordless, and I maintain the batteries for my cordless tools religiously).