Most milk jugs are high density poly ethylene, which resists gasoline and most other chemicals at room temperature. However, they are thin, cheap, disposable containers not formulated for a long life. The dairies have squeezed every possible penny out of our cost. I think they will embrittle stored empty in a cool, dark, dry place. I don't even try to reuse them for water.
Like Brian, I use detergent bottles for used oil. Apparently they are expected to last a little longer.
I would never hoard, but I did top up the car at $2.67 earlier this week and the truck at $2.64. Today, gas went up to $2.79. Didn't get stuck buying any of the $3+ stuff.