Moses, Aaaron, Nadab, Abihu, and seventy elders of Israel ate with God upon Mount Sinai.
With GOD's covenant with Israel having been sealed at Mount Sinai, GOD called Moses and 70 elders of Israel to eat in His presence on the mountain:
1 Now He said to Moses, “Come up to the Lord, you and Aaron, Nadab and Abihu, and seventy of the elders of Israel, and worship from afar. 2 Moses alone shall come near to God, but they shall not come near; nor shall the people go up with them.”
3 So Moses came and told the people all the words of God and all the ordinances, and all the people answered with one voice and said, “All the words the Lord spoke we will do.” 4 Then Moses wrote all the words of the Lord; and he rose early in the morning and built an altar at the foot of the mountain, and twelve stones according to the twelve tribes of Israel. 5 Then he sent young men of the children of Israel, who offered whole burnt offerings and sacrificed peace offerings of calves to God. 6 Moses took half the blood and put it in basins, and half the blood he poured on the altar. 7 Then he took the Book of the Covenant and read in the hearing of the people; and they said, “All the Lord said, we will do, and be obedient.” 8 Moses then took the blood, sprinkled it on the people, and said, “This is the blood of the covenant the Lord made with you according to all these words.”
9 After this, Moses went up, along with Aaron, Nadab, and Abihu, and the seventy of the elders of Israel; 10 and they saw the place where the God of Israel stood. Under His feet was, as it were, a paved work of sapphire stone and the appearance of heaven's firmament in its purity. 11 And of Israel's chosen men not one was missing. So they saw the place of God, and ate and drank.
(Exodus 24:1-11 OSB)
Ancient covenants were confirmed with a celebratory meal acknowledging the peace established by the agreement. So it was with GOD and Israel.
The text does not give us as many details as we might like. But it seems that GOD somehow provided this meal. Either this, or they carried the food with them upon the mountain, which the text does not indicate.
What the text does emphasize is the beauty of this place where GOD "stood," and that this visit was peaceful. Throughout Scripture, we see that ancient people were mortified that, if they saw GOD, they would die. GOD would later tell Moses:
20 But He said, “You cannot see My face; for no man can see My face and live.”
(Exodus 33:20 OSB)
So it was not a common thing, at that time, for humans to come this close to GOD.
These things were done to communicate the special nature of GOD's relationship with Israel through their newly-established covenant. They also provide meaningful shadows of future events that help us better understand and more deeply appreciate what Jesus did for us.