Thats the crux of the game....its only ONE item. What always gets me is that when asked this question usually people have a hard time picking just that one thing and a lot of times its also a toss up between the sentimental childhood toy that only means something to you personally vs. the really expensive something they have.
For me, I have a Dankin Dog (its a plush dog stuffed with crushed peanut shells.) They are quite rare but I've had mine literally since the day I was born. It was my very first toy ever and bought for me on my actual birthday and placed in the crib at the hospital. It's survived with me all these years and would be the one thing I would grab without question.
"Many Shubs and Zuuls knew what it was to be roasted in the depths of the Sloar that day I can tell you."