$5.00 Holiday Gift Certificate
To generate sales after Christmas, send a Christmas card to your customers to arrive right before Christmas (after they've purchased their holiday gifts), which includes a "Thank You For Your Business" gift certificate for $5.00 to be used only between December 26 and January 15th. Hold firm to the expiration date, and if you do this year after year, your customers will learn to use it in the 3 weeks right after Christmas. This should generate some sales early in the new year.
Updated! I adapted this idea and enclosed a coupon that offers $20 off with an $80 purchase or $10 off with a $40 purchase. We'll see how I do with this one.