The ornamental design for an expandablebag, as shown and described.
FIG. 1 is a top plan view of one embodiment of an expandable bag showing our new design in a non-expanded position, the bottom view being a mirror image thereof;
FIG. 2 is a front, left upper perspective view thereof;
FIG. 3 is a front, left upper perspective view thereof taken from an alternative angle;
FIG. 4 is a front, upper perspective view in an expanded position;
FIG. 5 is a front perspective view thereof;
FIG. 6 is a right side perspective view thereof; and,