The ornamental design for the self supporting card holder, that as shown.
FIG. 1 is a front perspective view of self supporting card holder showing my new design with the playing cards shown in dotted lines for illustration purposes only.
FIG. 2 is a top view thereof.
FIG. 3 is a side view thereof; and,
FIG. 4 is a front view thereof.
The broken lines are for illustrative purposes only and forms no part of the claimed design.