The industry continues to consolidate. If the FTC didn't block the Kroger deal on Albertsons, I'd imagine prices to be worse. So that basically leaves Walmart, Amazon, Target in the top 10. Excluding Costco, of course.
If you haven't seen the writing on the wall yet, as the US effectively splits up and global trade gets shut down, the future of food in America will revert to what it was for our great grandparents - local community gardens, farmers markets, buying clubs, direct farm to consumer, etc.