I’ll go first. Mine is the instant knockout drug. Like Dexter’s intramuscular injection that causes someone to immediately lose consciousness. Or in the movie Split where there’s the aerosol spray in your face that makes you instantly unconscious. Or pretty much any time someone uses chloroform.
Coffee/drink cups that have nothing in them. At least put water in them so they don’t look obviously empty. Lol
This can still be problematic for other reasons, like sound. But I agree, they need weight (or better actors…).