The ornamental design for a bag, as shown and described.
1. Bag
1.1: Perspective
1.2: Front
1.3: Back
1.4: Right
1.5: Left
1.6: Top
1.7: Bottom
1.8: Perspective
1.9: Perspective
1.10: Perspective of the bag open
The bag comprises a body and a shoulder strap; the body has a rectangular front wall and a rear wall which is also rectangular and extends towards the front of the bag so as to form the front flap which is also rectangular and covers the front wall of the bag; the latter has a horizontal retaining element that can be inserted all the way through a horizontal slit in the flap so as to be engaged by a mobile locking element of a locking mechanism attached to the flap; the front and back walls of the body are interconnected by two side pleats and a bottom pleat.