The ornamental design for a bag, substantially as shown and described.
FIG. 1 is an isometric view of a bag showing the top, front and right side thereof;
FIG. 2 is an isometric view showing the bottom, rear and left side thereof,
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof,
FIG. 5 is an elevation view of the left side thereof,
FIG. 6 is an elevation view of the right side thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The portions in the figures which are shown in broken lines are intended to show the environment in which the bag is used and do not form a part of the claimed design.