The oil used in the anointing is blessed in a little service at the close of Vespers in the Russian/Slavic tradition, along with wheat, wine and bread (these four being staples of life), during feasts of full Vigil rank. This is the prayer the priest chants for it:O Lord Jesus Christ our God, who blessed the five loaves in the wilderness, and satisfied the five thousand, bless these loaves, wine, and oil, and multiply them in this city, and in all Your world; and sanctify the faithful who partake of them. For it is You who blesses and sanctifies all things, O Christ our God, and to You we send up glory, together with Your Father, who is without beginning, and Your all-holy, and good, and life-creating Spirit, both now and forever, and to the ages of ages.
The five loaves thus blessed are then sprinkled with the wine, and cut up into pieces. Following the Gospel reading and Prayer of Intercession at Matins, the Canon(s) are chanted. Those attending the service line up, each person venerates the central icon of the saint or feast being commemorated, then stands before the priest, who paints a cross on the person's forehead with a small brush dipped in the blessed oil. The person then takes (or is handed) a piece of the blessed bread. Or, the blessed wine is diluted with warm water, and distributed to all.
As well as commemorating the miraculous feeding of the Five Thousand, the consumption of the bread and wine provides a little sustenance to help the faithful "endure" the remainder of the service. This would be particularly welcome during monastic vigils, devoid of the usual, accepted parish short cuts, which truly do go on all night. While I've never attended an eight-hour (or more) vigil, I have attended a few at a monastery that have run for four or five hours, and the chunk of bread and the small cup of warm diluted wine is, indeed, a tonic.