On Christmas Eve, Plutonians place favourite possessions under the Christmas tree, and a curious Reverse Santa sweeps down every chimney, hoovering up all the toys. Thus Plutonians learn the value of stoicism, important at the edge of the Solar System.
Next day, all Plutonians meet at the village hall to sort out and recover the gifts where they've all been dumped together in a heap. This is a great social event.