The ornamental design for a couponholder, as shown and described.
FIG. 1 is a perspective view of a coupon holder showing my new design, with
the broken line showing for illustrative purposes only and forming no part
of the claimed design;
FIG. 2 is an enlarged front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a side elevational view thereof, with the opposite side being a
mirror image; and,
FIG. 5 is a top plan view thereof, with the bottom being a mirror image.