It'd be nice to store some gasoline on hand, in the event of an emergency. However, there are three two problems:
1) most cities limit how much you can store.
2) storing a lot safely can be expensive (tank installation)
3) gasoline doesn't store terribly long
1) find out how much you can legally store (that includes amount, location, and type of container)
2) even a "little" can go a long way in the event of an emergency
3) now the fun part:
I purchased some 5-gallon gas cans from Home Depot and filled them at Costco (cheapest gas around for us). They're now in the garage. We have a van with a 17-gallon tank, and a Civic with a 14-gallon tank (I think). I've instructed Julie to never let the tank go below half before filling up again. Yes, it means more fillups, but it also means you'll always have a half-tank of gas in the event of an emergency.
I've now instructed Julie to never fill the van at a gas station, but to always fill it at home with the gas can(s). Then, she should take the empty cans, throw them in the van, and fill the cans.
In this way we:
1) always have gas on hand
2) don't have to worry about the gas going bad, as we're always rotating it
3) will avoid $35/gallon "generator" gasoline in the event of an emergency