I claim the ornamental design for a collapsible wagon, as shown and described.
FIG. 1 is a perspective view of a collapsible wagon in an assembled configuration, showing my new design with a portion of the handle shown broken away for the ease of illustration;
FIG. 2 is a front elevational view of the invention in the assembled configuration;
FIG. 3 is a rear elevational view of the invention in the assembled configuration;
FIG. 4 is a right-side elevational view of the invention in the assembled configuration, the left-side elevational view being a mirror image thereof;
FIG. 5 is a top plan view of the invention in the assembled configuration;
FIG. 6 is a bottom plan view of the invention in the assembled configuration;
FIG. 7 is an exploded right-side elevational view of the invention; and,
FIG. 8 is an exploded perspective view of the invention with a portion of the handle shown broken away for the ease of illustration.