In England Twelfth Night used to be one of the main seasonal feast days. After the Reformation less attention was paid to the feast of the Epiphany so Twelfth Night could be free of the religious connotations of Christmas Day. It was a time for dancing, singing, drinking and mumming, often with bawdy overtones.
A Twelfth Night Cake was an important feature, and the more ornately decorated the better. This traditions continues in other countries that do celebrate the Epiphany as a "Three King Cake."
Twelfth Night is also the last day for the Christmas decorations, including the mistletoe bough, so if it's been heavily laden with berries and there are plenty left, lots of kissing is required. On the 6th it must all come down. We'll be taking ours down tomorrow. Never say you've already taken down yours!
All best wishes for 2014.