鵝卵石 Willow Sprigs and River Pebbles
才叫沙僧：「你與哥哥哭著，等我去尋些甚麼供養供養。」他就走向澗邊，攀幾根大柳枝，拾幾塊鵝卵石。回至墳前，把柳枝兒插在左右，鵝卵石堆在面前。才叫沙僧：「你与哥哥哭着，等我去寻些甚么供养供养。」他就走向涧边，攀几根大柳枝，拾几块鹅卵石。回至坟前，把柳枝儿插在左右，鹅卵石堆在面前。
逐句解 Line by line
Only then did he call to Sha Monk, "You and our brother keep up the weeping, and let me go and find something for an offering."
供養 is to make offerings to the dead or to a deity, and the first character 供 is gòng for that sense — not the reading it takes in the sense of supporting living parents. The doubling of the word makes it casual, the way one might say sort out some sort of offering. Note also that he assigns the weeping to the others as a job.
So he walked over to the ravine, pulled down a few big willow branches, and picked up a few goose-egg cobbles.
鵝卵石, goose-egg stones, is still the ordinary Chinese word for a rounded river cobble — the same picture English reaches for with egg-shaped. Willow and stone are what the ravine has, and Bajie is working with what he can find.
Coming back to the grave, he stuck the willow sprigs in on the left and the right, and heaped the cobbles up in front.
The arrangement is a real one. A grave should have trees flanking it and an offering set out at the front, and Bajie is reproducing the layout of a proper burial with the wrong materials. The care is in the placing, not the goods.
Everything Bajie does here is correct in form and absurd in substance. A proper grave wants evergreens down each side and food set out in front, and he has willow twigs and pebbles from a stream.
The novel is setting up a joke, and it will let Wukong deliver it in the next passage. What it will not do is let the joke be simple, because Bajie's answer to the mockery turns out to be better than the mockery.