Can I eat before the sobor?
Yes, you can eat before Soborovanie. There are no special rules for this count. Most importantly, during the Soborovanie, sincerely ask the Lord to forgive you of your sins and help in healing. After the Sobor you have to confess and receive Communion within a week.
The unification of the Holy Priesthood is called the Elenology, and this Mystery represents the sevenfold anointing with oil, which was sanctified by priestly prayer. In this way, God's help for the healing of various ailments will be given to all people: both the spiritual and the physical plan.
But as far as food is concerned, you can eat before the cathedral and afterwards: