Costco (NASDAQ: COST) has been a big winner so far this year. Consumer staples stocks have generally had a good year, with the Consumer Staples Select Sector SPDR Fund (ARCA:XLP) providing a total return of 15%. However, that still lags the over 20% return of the S&P 500. Costco has particularly impressed. Its 33% total return this year surpasses its sector and the industry by a wide margin. So, what has been driving Costco’s recent success, and is there still room for this stock to run? Breaking Down Costco’s Revenue StreamsMost everyone knows about Costco’s business model. The company buys a…