The ornamental design for “bag with window and opaque flap,” as shown and described.
FIG. 1 is a top view of the bag with window and opaque flap.
FIG. 2 is a bottom view of the bag with window and opaque flap.
FIG. 3 is a front view of the bag with window and opaque flap.
FIG. 4 is a back view of the bag with window and opaque flap.
FIG. 5 is a right side view of the bag with window and opaque flap.
FIG. 6 is a left side view of the bag with window and opaque flap; and,
FIG. 7 is an elevational view of the bag with window and opaque flap.
The broken line showing of portions of the bag are included for the purpose of illustrating environmental structure and forms no part of the claimed design.