NEW YORK — Fall was a dismal season at retail and now, this industry is in the throes of the most challenging Christmas season in a generation. Still, shoppers are hitting — and in some cases, packing — the stores as the calendar winds down to Santa time. Today WWD begins a week-long look at what’s selling, including the emergence of a number of trends. Case in point: the red-hot red leather bag. Here, from left, bags from Christian Dior, $775; Coach, $298; Hermes (back), $2,675, and Tod’s (front), $1,100.