The ornamental design for a bag, as shown and described.
FIG. 1 is a perspective view of the front, top and one side of the bag showing my new design, the other side being the same;
FIG. 2 is a perspective view of the rear, top and one side thereof;
FIG. 3 is a perspective view of the front, top and one side thereof, with the body thereof being in a closed position and the top cover thereof being in an open position;
FIG. 4 is a perspective view of the front and one side thereof, with the body and the top cover thereof being an in open position; and,
FIG. 5 is a plan view of the bottom thereof.
The broken lines showing the shaft portion of the handle are for the purposes of illustrating environment and forms no part of the claimed design.