I claim the ornamental design for a bungee cord keeper, as shown and described.
FIG. 1 of the drawings is a perspective view showing the front, left side, and top of a bungee cord keeper embodying the design of my invention;
FIG. 2 is a front elevation view of the bungee cord keeper;
FIG. 3 is a left side elevation view;
FIG. 4 is a top plan view;
FIG. 5 is a right side elevation view;
FIG. 6 is a back elevation view;
FIG. 7 is a bottom view; and,
FIG. 8 is another perspective view of the bungee cord keeper shown reduced in size and in its usual bungee cord environment. The broken lines depict a typical bungee cord and they form no part of the claimed design.