Depends, is it a casual thing or more serious? If it’s casual I’d probably just bring a Trading Card Game deck (MTG, YuGiOh, Pokémon). If it’s more serious, I’d bring in some of my junk like a broken microwave magnetron, to simultaneously bring attention to the problem of short product cycles, explain a bit about how what most people see as a magic appliance functions, and show that even complex things can be broken down into simple parts.