we Orthodox Christians prepare for each major event in the Church year in fasting and repentance. Fasting must be understood as abstention. We strictly abstain from all animal products (including dairy), wine and oil. However, the Nativity Fast is one of the least restrictive. There are many Wine and Oil days (WO), and many Fish, Wine and Oil (FWO) days.
The music of our Fasts frequently is both beautiful and somewhat mournful. Here is some of the Music of Nativity from the Russian Orthodox Church.