Rent the Runway’s sales grew 40 percent year over year, and its subscribers are more likely to stick around after one year than those of Stitch Fix.

By raw dollars, Nike sales have increased more than competitors' this year. But Adidas is making a strong digital push, with annual sales up nearly 40 percent year to date.

Prime Day 2018 promises deals that rival Black Friday and a boost for Amazon’s subscriber base, which accounts for three-quarters of its U.S. sales.