What, though flat, has the power to fill and empty pockets, yet never carries anything itself?

Many look for me in the evening to see what they have achieved. I lack my own legs, yet I follow you step by step, all day long. Solve the riddle → I can be worth a lot on one side of a border and less on the other, even though I look the same. What am I? Solve the riddle → What swallows trees and spits out paper, sometimes with a low-level warning? Solve the riddle → What gathers the family's messiest secrets behind a closed door, only to spit them out clean and shining? Solve the riddle → Many stand in line for me, but I have no legs. I can grow long, yet still be invisible. Solve the riddle →