The ornamental design for an outdoorbackpack, as shown and described.
FIG. 1 is a perspective view of an outdoor backpack showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is an enlarged view of portion 9 shown in FIG. 1.
The broken lines in the drawings depict portions of the outdoor backpack that form no part of the claimed design. The unevenly dashed broken lines in FIGS. 1 and 9 depict the cut line of the enlarged section and form no part of the claim design.