FIG. 1 is a top front perspective view of a bag showing the claimed design in an open configuration; FIG. 2 is a front view thereof in a closed configuration; FIG. 3 is a rear view thereof; FIG. 4 is a right side view thereof, the left side view being a mirror image thereof; FIG. 5 is a top view thereof; and, FIG. 6 is a bottom view thereof. The broken lines in the figures show portions of the bag that form no part of the claimed design.