Our Druid ancestors called the equinox "Alban Elfed" has a beautiful poetic sounding name, I think, and it means "the light of the water", again a beautiful image which refers to it being the time of year when the balance of light and dark shifts from being primarily the light of day to primarily themdark of night.
Mabon is the name given to this feast day in the modern Paganism. Ronald Hutton, one of my favorite historians, has pointed out that there is no evidence it was ever called Mabon by the ancient Celts. The used of Mabon only goes back to about 1970, and was included in Aiden Kelly's 1991 book "Crafting the Art of Magic", where he replaced the old names of Pagan holidays with new names with Celtic roots.
Where does the word Mabon come from?
In Welsh folklore, there is a figure known as Mabon ap Modron, or Mabon son of Modron. He appears in some of the Arthurian legends, as one of Uther Pendragon’s loyal servants, and as a follower of Arthur himself.Also of note, there was a female Cornish saint named Mabyn, to whom the founding of St. Mabyn’s Church is dedicated, although there is speculation that the church was actually started by the Welshman, Mabon, rather than the female martyred saint. Mabyn’s festival is celebrated on November 18, approximately halfway between the autumn equinox and the winter solstice.
People, being social beings, created celebrations around these dates, I would guess that beyond ceremonies of thanksgiving and petitioning for blessings in coming season, convivial reflection on the bounty of the season, each holy day had prayers and ceremonies unique to it.
Mabon is a bit like a bridge between the abundance of summer and the bleak winter, and perhaps this lead to prayers for a balance in daily life, meaning that there should be no catastrophic events, that would cause the physical and/or spiritual world to collapse.
With the certainty of winter approaching, perhaps there were prayers to bless and protect home and property not only from the harsh weather and storms but from intruders and marauders, disease, possibly even the ravages of age. These probably mingled with petitions for the return of lengthening days and warmer weather.
In places where grapes were apart of the harvest most certainly wine was part of the celebration. Farther north there were the beverages made from John Barley Corn. Both from recently harvested crops, must have been welcome additions to the table fare and reason for thanksgiving. The Equinox celebration was probably not one of the solemn holy days, and depending on who you read, was at least partially centered on friends, family and community.