Albert Barnes Commentary 1 Samuel 30:20

"And David took all the flocks and the herds, [which] they drove before those [other] cattle, and said, This is David`s spoil." — 1 Samuel 30:20 (ASV)

The meaning is that David took all the sheep and oxen that the Amalekites drove—that is, the livestock they possessed before the cattle they acquired in their recent raid to the south. The people then declared, "This is David's spoil." This was his share as captain of the band .

All the other plunder of the camp—arms, ornaments, jewels, money, clothes, camels, and equipment—was divided among the small army. David's motive in choosing the sheep and oxen for himself was to make presents to his friends in Judah (1 Samuel 30:26–31).