The ornamental design for a fresh-keeping bag, as shown and described.
FIG. 1 is a front and top perspective view of a fresh-keeping bag, showing my new design;
FIG. 2 is a rear and bottom perspective view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a right side elevation view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is an enlarged view of region 9 in FIG. 1; and,
FIG. 10 is an enlarged view of region 10 in FIG. 2.
The dash-dot-dash broken lines framing portions of the claimed design in FIGS. 1, 2, 9 and 10 that are illustrated in enlargements form no part of the claimed design.