A "trap sack" is a slang term for a personal stash bag where someone keeps items they don't want others, such as their mom or TSA, to find. It often contains things like a secret stash or personal belongings that are meant to be hidden or kept discreet. It is essentially a bag used for concealing and carrying things you want to keep private or out of sight. In some contexts, it can refer more broadly to a bag used to carry various items you want to hide or keep secure from others' knowledge or discovery. So, a trap sack is basically a secret or personal stash bag to hold things you do not want others to see or find.