The ornamental design for a bag, as shown and described.
FIG. 1 is a front and left perspective view of a bag showing my new design;
FIG. 2 is a front plan view of the bag illustrated in FIG. 1;
FIG. 3 is a rear plan view of the bag illustrated in FIG. 1;
FIG. 4 is a right side plan view of the bag illustrated in FIG. 1;
FIG. 5 is a left side plan view of the bag illustrated in FIG. 1;
FIG. 6 is a top plan view of the bag illustrated in FIG. 1;
FIG. 7 is a bottom plan view of the bag illustrated in FIG. 1;
FIG. 8 is a cross-section view of the bag illustrated in FIG. 1; and,
FIG. 9 is a cross-section view of the bag illustrated in FIG. 1.
The dash-dash-dash-dash type broken lines shown in the drawings are included for the purpose of illustrating environmental structure and form no part of the claimed design.