"The guy is constantly eating. I don't know how he's in such good shape," Jackson said.
Other staples include peanut M&Ms, Cherry Coke Zero and chunky organic peanut butter for his favorite snack: peanut butter-and-honey sandwiches.
As a Mormon, Romney drinks neither coffee nor beer, but stocks both on his campaign bus for others. Jackson revealed a case of Miller Lite in the fridge that he attributed to traveling press secretary Rick Gorka.
The 25-year-old Jackson has been at Romney's side as his personal assistant since shortly after graduating from the University of Mississippi in 2009.
He describes his relationship with the GOP nominee as "like [an] uncle and adoring-nephew type."
Jackson has been called upon to steady chairs the former governor stood on to give a speech, and last week, he joked in a tweet that he played "chaperone" on Mitt and Ann Romney's date to the Alfred E. Smith Memorial Foundation Dinner, a white-tie affair. Jackson's tweets @dgjackson are the best source for behind-the-scenes pictures and updates on the campaign trail.
"I feel like I have one of the coolest jobs in the world," he told CNN.