The ornamental design for a lunchcooler, as shown and described.
FIG. 1 is a perspective view of the lunch cooler;
FIG. 2 is a front view of the lunch cooler;
FIG. 3 is a rear view of the lunch cooler;
FIG. 4 is a right side view of the lunch cooler;
FIG. 5 is a left side view of the lunch cooler;
FIG. 6 is a top view of the lunch cooler; and,
FIG. 7 is a bottom view of the lunch cooler.
The broken lines showing in the figures are included for the purpose of illustrating portions of the lunch cooler that form no part of the claimed design.