‘And Jacob offered a sacrifice in the mountain, and called his brothers to eat bread, and they ate bread and tarried all night in the mountain.'
The offering of sacrifice to seal a covenant is well known (see Genesis 15). Compare the words of a government official to Zimri-Lim of Mari (18th century BC) “I have killed the ass with Qarni-Lim, and thus I spoke to Qarni-Lim under the oath of the gods. ‘If you despise Zimri-Lim and his armies I will turn to the side of your adversary'.” There too a covenant of peace was involved.
This is Jacob's response to Laban's offer. By offering sacrifice and eating with the confederate leaders he fully accepts his part in the covenant, while their eating with him is a sign of their peaceful acceptance of the terms. All are now agreed and the deed is done. The feast goes on through the night (compare Genesis 24:54).