The ornamental design for a combinationcoaster and displaycase, as shown and described.
FIG. 1 is an isometric view of a combination coaster and display case showing my new design.
FIG. 2 is a front view thereof, the rear view being identical.
FIG. 3 is a right side view thereof, the left side view being identical.
FIG. 4 is a top plan view thereof.
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is an exploded top perspective view thereof.
Those portions of the figures that are presented in broken lines merely illustrate the environment of the design and are not part of the claimed design.