I claim the ornamental design for a bag, as shown and described.
FIG. 1 is a rear view of a bag according to my new design;
FIG. 2 is a front view of the bag shown in FIG. 1;
FIG. 3 is a bottom view of the bag shown in FIG. 1;
FIG. 4 is a top view of the bag shown in FIG. 1;
FIG. 5 is a right side view of the bag shown in FIG. 1;
FIG. 6 is a left side view of the bag shown in FIG. 1;
FIG. 7 is a front perspective view of the bag shown in FIG. 1; and,
FIG. 8 is a rear perspective view of the bag shown in FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. Any broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.