The ornamental design for a usbmemorystick, as shown and described.
FIG. 1 is a Top, front, right side perspective view of USB memory stick, showing our new design;
FIG. 2 is a Bottom, rear, left side perspective view thereof; and,
FIG. 3 is a Top, front, right side perspective view thereof, with the cap removed.
The broken line showings of the connector and cavity in the cap are included for the purpose of illustrating portions of the USB memory stick and form no part of the claimed design.