Why is Dan called "Me'asef le'Chol ha'Machanos"?
Rashi #1 (citing the Yerushalmi in Eruvin, 5:1, according to the opinion that they traveled like a box 1 ): Since Dan was the (second) 2 largest tribe, they traveled in the rear, where they spread out and were therefore in a position to pick up all the lost articles that the other tribes had dropped.
Rashi #2 (According to the opinion that they traveled (one behind the other) like a bea. 3
Rashi #3 (in Yeshayah, 2:12): Those who travel at the back are called 'Me'asef' because they pick up all the stragglers.