In Massachusetts the plastic bag is mandatory, as is the aluminum foil.
What a great state to live in.
At least we can still drive a car at at 65 MPH while text messaging.
Of course, they didn't define what a "cannon" is in the regulations so at some undefined point it is so small it is no longer a cannon but a muzzleloading handgun and the regulations won't apply.
Anyway, BP is not all that static sensitive. There are some sources of data on the net that seem to prove this to some degree. It is actually possible to occationally buy it in bulk, usually of chinese origin, in plastic bags packed in cardboard boxes.
The reason for the requirement, right or wrong, is that the plastic bag will contain the BP and make sure than none works it's way out of the various folds in the aluminum foil.
As far as plastic residue, I always find the bottom half of the aluminum foil bag in the bottom of the bore but have never found even a hint of the plastic bag anywhere. I always assumed it vaporizes.
Rick