Snapping sounds like a real faff.

Keep them all in a special plastic box that is inside a powerful electromagnet.

Push button and a field that is strong enough to damage the cards almost instantly and over a short time would generate enough heat to physically damage the cards.

With enough power and time you could turn them into one hot blob that wouldn’t even be recognisable.

So near instant data damage and then physical destruction probably before someone can work out what’s going on.