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 : Enlarged detail of the open bag
The bag comprises a gusseted body open towards the top, and a shoulder strap; the body has a front panel and a rear panel, each of which is provided with a rod at the top; a rod is provided at its ends with rings, to which are connected the ends of the shoulder strap; the sequence of figures shows the bag in perspective view, front view, rear view, right-hand view, left-hand view, top view, bottom view, an enlarged detail of the closed bag and an enlarged detail of the open bag; the dash-dot line in reproduction 1.8 depicts bounds of the partial view only and forms no part of the claimed design.