The ornamental design for a stackablestockbox with openable end, as shown and described.
FIG. 1 is a right-side elevational view of a stackable stock box with openable end showing my new design, the left-side view being a mirror image thereof;
FIG. 2 is a front view thereof;
FIG. 3 rear elevational view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a top perspective view of a stackable stock box with openable end with the front end open;
FIG. 7 is a bottom front perspective view of a stackable stock box with openable end with the front end closed;
FIG. 8 is another top front perspective view thereof;
FIG. 9 is a top rear perspective view thereof; and,
FIG. 10 is a large scale partial perspective view of stackable stock box with openable end with the front end open.