I would ask him to sing Just Pretend to me. & I would want him to sing (and join in with..) King Of The Whole Wide World.
I would love to have been to the Tupelo show in 56. Otherwise, the 68 Special.
A momento, Domino ? (is that allowed! ) Priscilla wouldnt be happy would she. If not, something personal, like a ring. And I would ask Joe or someone to take a photo of me 'n' Elvis!!