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 showing of the connector is included for the purpose of illustrating portions of the USB memory stick and forms no part of the claimed design.