I was visiting my left-leaning son and his flaming-liberal girlfriend recently in Pittsburg (they attend CMU).
Anyway, he and I went to the grocery store and bought, among other things, a couple of portobello mushrooms for his girlfriend. He was going to carry them in his hands for a couple of blocks back to their place rather than get a small plastic bag to carry them. I would have none of it and put them in a bag for him.
The engineer in me wouldn’t let it go.
So, I asked him: “How much oil do you think it takes to make a plastic bag like this?”
His answer: “Some, I guess. I don’t know.”
My response: “Here’s a hint. Consider the weight of this plastic bag. The weight is essentially the same before and after. You can measure the amount of oil needed to produce it in ‘drops of oil’.”
cheee
Also plastic bags are made of polyethylene which is a pure hydrocarbon, nothing but carbon and hydrogen atoms, so unlike other plastics it is safe to burn or re-use in a fuel. All the energy content of the original petroleum used to make the bag is still there. Possibly the waste heat of a diesel engine, such as a store’s delivery truck, could be used to efficiently turn these bags into diesel fuel. But like you said it would only be a couple drops of oil per bag.