The ornamental design for commuter bag, as shown and described.
FIG. 1 is a front elevation view of a commuter bag of the present invention;
FIG. 2 is a right side elevation view thereof;
FIG. 3 is a left-back perspective view thereof; and,
FIG. 4 is a front elevation view thereof in a position of use.
The bottom part of the commuter bag does not form part of the claimed design.
The broken line showing is included for the sole purpose of illustrating environmental elements for the commuter bag and forms no part of the claimed design.