The ornamental design for a soft-sided shopping bag, as shown and described.
FIG. 1 is a perspective view of the soft-sided shopping bag from above the bag, showing the front and left side, the back and right side being respective mirror images of the front and left side and the interior and exterior surfaces of each of the walls defining the front, back and sides being the same; and,
FIG. 2 is another perspective view of the bag of FIG. 1 from above the bag with the elastic sides expanded to their fullest extent, showing the front and left side, the back and right side being respective mirror images of the front and left side.
The broken line showing, in the views, is for illustrative purposes only and forms no part of the claimed design.