The ornamental design for a bag-double layer foldable pencil bag, as shown and described.
FIG. 1 is a perspective view of a bag-double layer foldable pencil bag embodying the new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back 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 new designs for a perspective view of a storage bag.
The broken lines in the drawing figures showcased on the upper surface depict stitching which forms no part of the claimed. Further, the broken line depict the slider also form no part of the claimed design.