The ornamental design for a handle for backpack or luggage, as shown and described.
FIG. 1 is a right side perspective view of a handle for backpack or luggage, showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a second perspective view thereof, shown in environmental use.
The broken lines shown represent unclaimed subject matter and form no part of the claimed design. The dotted lines shown represent stitching and form part of the claimed design.