Peter Lynch once said retail investors should “invest in what you know,” and it’s likely that a lot of readers will have shopped at either Kroger (NYSE: KR) or Costco (NASDAQ: COST) recently. Kroger is the largest pure-play supermarket in the country, operating under brand names Kroger, Ralphs, King Soopers, and others. Meanwhile, Costco is the largest discount wholesale membership club, with 90.3 million members as of its most recent quarter.