The ornamental design of a covering for an insulating can cooler, as shown and described.
FIG. 1 is a front view of my new design of a covering for an insulating can cooler, the rear view being identical;
FIG. 2 is a top view of my new design, the bottom view being identical; and,
FIG. 3 is an elevated front view of my new design.
The insulating can cooler shown in broken lines in the figures forms no part of the claimed design. The illustrated embodiment is formed from a woven bamboo material to embody the claimed design.