Gap has announced on their facebook page that everything in-stores will be 40% off, Saturday only. Here are the important details:

When: Saturday, November 20 · 9:00am – 10:00pm
Where: All U.S. and Canada Gap, GapKids, babyGap and GapBody locations only
This Saturday only save 40% off the entire store, including sale merchandise. All existing Gap, BR or Old Navy cardmembers will receive 45% off when they use their Gap, BR or Old Navy Credit Card.
To save 40% just mention FLASH40 at the register. Mention FLASH45 if you have a Gap, Banana Republic or Old Navy Credit Card.
Offer valid at Gap Stores in the U.S. and Canada Only. Not valid at Outlet/Factory stores or gap.com. No adjustments on previous purchases. Not valid for cash or cash equivalent. Gap, Banana Republic or Old Navy Credit Card must be used to receive 45% off. Cannot be combined with any all other promotions or MPC discounts.