The ornamental design for a lunchbag, as shown and described.
FIG. 1 is a back view of a lunch bag, showing my new design.
FIG. 2 is a front view of the lunch bag of FIG. 1.
FIG. 3 is a left side view of the lunch bag of FIG. 1.
FIG. 4 is a right side view of the lunch bag of FIG. 1.
FIG. 5 is a top view of the lunch bag of FIG. 1; and,
FIG. 6 is a bottom view of the lunch bag of FIG. 1.
The evenly spaced broken lines on the lunch bag in FIGS. 1-4 represent stitching. The remainder of the broken lines in the drawing views depict portions that form no part of the claimed design.