They will tell you that everything they need is between the 2 covers of the bible. If it is not there they don’t need it for salvation.
What about the second part of my idea / my other idea. Show them various writings, have challenge them to defend their status as Biblical or apocryphal. I suggest:
*Genesis, to represent the Pentateuch
*Judges, to represent the historical books
*Psalms, to represent the wisdom books
*Isaiah, to represent the prophets
*(Greek) Esther, to represent partially deuterocanonical books
*Wisdom, to represent purely deuterocanonical books
*Luke, to represent the synoptic gospels
*John, as the non-synoptic gospel (which, for extra fun, contains John 1:1 and the Bread of Life discourse)
*1 Corinthians, to represent the undisputed epistles
*James, to represent the epistles Luther tried to remove
*Revelation, as the odd book out in the NT
*The Protoevangelium of James, as a popular apocryphal gospel (and IIRC the source of Anne and Joachim’s names)
*The Didache, as a book that, IIRC, really only didn’t make it in because it was too young
*The Gospel of Thomas, as a gnostic gospel
*Enoch, as an OT apocryphal book, with the added bonus of being referenced in the epistles
*1 Esdras, to represent that books of the capital-A Apocrypha that aren’t in deuterocanon.
Yeah, quite the list. 16 books. But I think it covers all the bases for debating what is and isn’t in the Bible.