The difference between bikeshedding and engineering is just that the engineer cares to get these details as right as it makes sense, and then continue with the work. Whether glass bottles are better energy and emissions-wise than disposable plastics is a question that needs to be asked and answered, and anyone pretending it's not relevant is not a good environmentalist.

Similarly, with styrofoam vs. paper cups, it's something that could be first estimated and then either ignored (if the difference is within margin of error) or acted upon.