Backpack

FIG. 1 is a front, right perspective view of a backpack showing my new design; FIG. 2 is a front elevation view thereof; FIG. 3 is a rear elevation view thereof; FIG. 4 is a left side elevation view thereof; FIG. 5 is a right side elevation view thereof; FIG. 6 is a top plan view thereof; FIG. 7 is a bottom plan view thereof; and, FIG. 8 is a front elevation view shown in an alternative configuration with patches adhered to the front of the bag. The broken lines depict portions of the backpack that form no part of the claimed design.