United Airlines has pretty simple holiday online mall shopping bonus. You need to have cumulative spend of at least $250 between 11/18-12/31 to be eligible for 1000 bonus miles. This is in addition to the miles you earn from actual purchase(s). Apparently, there is even no need to register for this.
You can visit United’s online shopping mall at https://www.mileageplusshopping.com/promo____.htm.