> Don’t we pass someone walking with a gas can on the highway every year though?

No. I see something like that every year on television, but not in the real world. If you've seen something like that every year, let me ask you a question: was the gas can empty or full? Gait while lugging five gallons of gas looks very different than gait while slinging around an empty can. Then, ask yourself whether or not you (or anyone you know) carries around a spare gas can in their vehicle.