Of the many contenders for Fall's must-have bag — and there are many — Marni's just-released Sculpture bag makes a pretty strong case . . . literally. Its lines are lean, its colors pure, and — with its structured shape and sleek metal handle — it falls right in line with the season's forward-marching mood. Priced from $1,050 to $2,160, the line is available at Marni stores and Marni.com now.