I'm not sure I understand why if the lights go out coins would be more advantageous than paper money, at least not the new dollar coins. Gold coins or silver coins I can understand but the new dollar coins have no appreciable precious metal value so in essence they would be no better than paper cash.

As for vending machines, if the lights were out the vending machines would be useless and besides in that situation I would not waste money on a vending machine I would simply break the glass to access the contents.