Gas doesn't "keep" without additives, and even then it's not likely to last more than a year or two... and you have the non-trivial costs of _properly_ storing it, in a way that's not a fire or chemical health hazzard, etc.
If you want to stockpile for when the **** hits the fan, buy lots of ammo in common sizes, even if you don't have a gun that can fire it. Excellent bartering material.
--Bushytails