I’ve never seen any of the phenomena you describe as being from Chutz La’aretz. I’ve always seen the kohanim taking their shoes off in the BM, and I’ve always seen them putting them right back on.
As far as plastic bags, the Mishneh Berurah does say that socks need not be taken off, so that might also apply to plastic bags. On the other hand, things that attract the eye’s attention to the feet or hands may not be worn (because they cause hesech hada’as on the part of the kehilla), so plastic bags might fall under that category.