Amazon.com is working on a drive-thru grocery concept that could be a serious threat to Publix Super Markets Inc. In the new Amazon concept, customers would order their groceries online, then pick them up at a drive-thru store , the Silicon Valley Business Journal , a sister news organization, reported Thursday. The first location would be an 11,600-square-foot drive-thru store, and the e-commerce giant will likely roll out multiple stores, according to SVBJ .