Every king has his crown, but for Duck Dynasty star Si Robertson, the one item he can't live without is his blue Tupperware cup -- preferably filled with iced tea. Robertson explains the full story behind his unusual accessory for the first time in his new book, Si-cology: Tales and Wisdom from Duck Dynasty's Favorite Uncle.

Robertson first acquired the blue Tupperware container when his mother sent it to him in a care package during his time serving in the military in Vietnam.

"Somehow, Momma's iced tea cup stayed with me all the way through Vietnam, and I've carried it in my back pocket ever since," he writes. "I guess if it can make it through the napalm, mustard gas, and rice wine of Vietnam, I'll probably take it to my grave."

Fame hasn't changed that resolve. Robertson says he never lets the cup out of his sight, and he wouldn't part with it for the world.

"One time, a guy handed me a blank check and wanted to buy my iced tea cup," he claims. "'Fill in the amount,' he said. 'Whatever it takes. I want that Tupperware cup.'"