We claim the ornamental design for a bag, as shown and described.
FIG. 1 is a perspective view showing our design for a bag;
FIG. 2 is another perspective view thereof;
FIG. 3 is another perspective view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a back elevation view thereof;
FIG. 6 is a left side elevation view thereof;
FIG. 7 is a right side elevation view thereof;
FIG. 8 is a top plan view thereof; and,
FIG. 9 is a bottom plan view thereof.
In the drawings, the long dashed broken lines showing a handbag depict environment and form no part of the claim. The short evenly dashed broken lines in the figures depict stitching and form no part of the claim.