The ornamental design for a flask and refill, as shown and described.
FIG. 1 is a perspective front and top view showing the flask and refill of our new design.
FIG. 2 is front view thereof.
FIG. 3 is a bottom view thereof.
FIG. 4 is a top view thereof.
FIG. 5 is a perspective front and top view showing the refill.
FIG. 6 is front view thereof.
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a top view thereof.
The broken lines in the drawings showing the bottom surfaces of the flask and refill illustrate the portions of the design that form no part of the claim.