The paper bag and sandwich was just an example. I've been thinking about it during the day and think I have a nice workaround that will work for the cave jam. Each container has a boolean variable to indicate whether it's open or closed. It's initially closed. Examine tells you whether it's open or closed. When you first open it, the contents fall out. You can't put it back in. You can close the container. When you reopen it, it will say it's empty. The puzzles related to this aren't complex, but the containers are needed for realism. You'll see what I mean in due course.
I like your suggestion about the dummy room. I was thinking of this myself, but, as you said, it really requires multi-word input and that's outside the scope of the jam.
Can't wait to get home and try this.