I have noticed that when the janitors come around to empty people's trash cans (which typically occurs once or twice a day), they often take out the plastic bag with the trash in it and put a new bag on the trash can. This is wasteful both with regard to the cost of the plastic bags and the external cost to the environment. Most of the time it would be perfectly acceptable for the janitors to simply dump out the contents of the trash can without replacing the bag. I have seen them do this at times, but generally they do not, so I'm guessing that the cleaning crews are given no formal instructions as to when they should or shouldn't.
I recommend that agency policy stipulate that the plastic trash bags be replaced on a less-frequent basis. Perhaps just once a week, as well as upon the employee's request or janitor's discretion at any time in between (i.e. whenever the circumstances dictate; for example, when there's some residue on the bag that looks like it might attract pests), or some other frequency that makes sense. This idea could be implemented at any federal agency and would save literally millions of plastic bags from being used each year.