The design is the visual features of the FLIP TOP CAP shown in the drawings, whether those features are features of one of shape, configuration, ornament or pattern or are a combination of any of these features. Variants are included.Drawings of the design in twenty-five (25) views are included in which:FIG. 1 is a front perspective view of the FLIP TOP CAP in accordance with the subject design;FIG. 2 is a top elevation view of the FLIP TOP CAP of FIG. 1;FIG. 3 is a front elevation view of the FLIP TOP CAP of FIG. 1;FIG. 4 is a right side elevation view of the FLIP TOP CAP of FIG. 1;FIG. 5 is a front perspective view of the FLIP TOP CAP of FIG. 1 with the FLIP TOP CAP in the open position;FIG. 6 is a front perspective view of a variant of the FLIP TOP CAP in accordance with the subject design;FIG. 7 is a top elevation view of the FLIP TOP CAP of FIG. 6;FIG. 8 is a front elevation view of the FLIP TOP CAP of FIG. 6;FIG. 9 is a right side elevation view of the FLIP TOP CAP of FIG. 6;FIG. 10 is a front perspective view of the FLIP TOP CAP of FIG. 6 with the FLIP TOP CAP in the open position;FIG. 11 is a front perspective view of another variant of the FLIP TOP CAP in accordance with the subject design;FIG. 12 is a top elevation view of the FLIP TOP CAP of FIG. 11;FIG. 13 is a front elevation view of the FLIP TOP CAP of FIG. 11;FIG. 14 is a right side elevation view of the FLIP TOP CAP of FIG. 11;FIG. 15 is a front perspective view of the FLIP TOP CAP of FIG. 11 with the FLIP TOP CAP in the open position;FIG. 16 is a front perspective view of another variant of the FLIP TOP CAP in accordance with the subject design;FIG. 17 is a top elevation view of the FLIP TOP CAP of FIG. 16;FIG. 18 is a front elevation view of the FLIP TOP CAP of FIG. 16;FIG. 19 is a right side elevation view of the FLIP TOP CAP of FIG. 16;FIG. 20 is a front perspective view of the FLIP TOP CAP of FIG. 16 with the FLIP TOP CAP in the open position;FIG. 21 is a front perspective view of another variant of the FLIP TOP CAP in accordance with the subject design;FIG. 22 is a top elevation view of the FLIP TOP CAP of FIG. 21;FIG. 23 is a front elevation view of the FLIP TOP CAP of FIG. 21;FIG. 24 is a right side elevation view of the FLIP TOP CAP of FIG. 21; andFIG. 25 is a front perspective view of the FLIP TOP CAP of FIG. 21 with the FLIP TOP CAP in the open position.