The arava on Shabbos was just like the weekdays except for the gathering of the willow branch which was done before Shabbos. Then they put the willow branches in a golden utensil which had water in it so they would not wilt.

R’ Yochanan ben Beruka says that on the 7^th day, a palm branch was used. They hit the branch on the ground near the mizbaiach.

Succa 4:7

After they finished the mitzvah on the 7^th day, the children would put aside the lulav and would eat the esrog.