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 : Front with offset flap
1.9 : Front with open flap
1.10 : Perspective with open back pocket
The bag comprises a body and a shoulder strap; the body has a front flap with a trapezoidal contour flared upwards; the lower end of the flap has an substantially horizontally elongated H-shaped relief pattern; the bag further comprises a clasp with a substantially horizontally elongated H-shaped relief catch element; the ends of the shoulder strap are coplanar with the front surface of said body; the seams of the bag are not claimed features.