"Today is the day of Lights and illumination...."
The Feast of Theophany (or Epiphany; or Feast of Lights), which essentially closes the holy Twelve Days of Christmas (and is followed by the honorary celebration of the Synaxis of the Forerunner, because St. John the Forerunner first met Christ at His Baptism and played a significant role in it), is one of the biggest feasts of our Orthodox people, with rich folklore, which of course is dominated by the sanctification of the waters, the diving for the Cross in seas and lakes and rivers, the blessing by priests of homes and places of work and fields and even automobiles and agricultural machinery, among other things.
An old Greek folk tradition states that on the Feast of Theophany the Kalikantzaroi depart. Kalikantzaroi are said to be small demon-like creatures who reside in the bowels of the earth and escape after Christmas, and during the Twelve Days of Christmas they pester and bother people, looking for sausages and sweets. They would only depart after the waters have been sanctified by the priest. Of course, this is all part of Greek folklore and mythology, though it is based on the truth that every demonic presence is rid of with the sanctification of the waters.
The most important custom for Januaury 5th, the eve of Theophany, is that it is a day of preparation and strict fasting. In fact, it is such a strict fasting day that no oil is permitted, together with no meat, fish, eggs or milk. Basically it is a day to eat vegetables and legumes with no oil.
This day of strict fasting is partly our preparation to drink the Holy Water from the Service of the Great Blessing of the Waters on January 6th, the Feast of Lights. Although we do not fast to drink the Holy Water necessarily, but to prepare to properly celebrate the Theophany and receive the Body and Blood of Christ in the Theophany Divine Liturgy. This is because fasting between Christmas and Theophany is prohibited by the Church, therefore the Church set aside only one day to especially help Christians prayerfully focus on the significance of this Great Feast of the Church.
In Crete, where this tradition is still alive by many, they prepared on Theophany Eve a Lenten meal with no oil called "fotokolyva" or "papoudia". It was boiled wheat (kolyva) with various beans like fava and lentils, generally any type of bean found in the house, that was served for the eve of the Feast of Lights (Foton). They boiled and ate it with salt, accompanied by bread, onion, olives, etc. (when we fast we can eat olives for nourishment but not olive oil). They would also give the fotokolyva to the birds, such as the chickens and pigeons, together with the animals of the house like the cattle, because the cattle plowed the fields to sow the wheat and legumes. It was considered necessary for them to taste the fruit of their labors.
Below are further resources for the Feast of Theophany: