Just to say - thanks for the question!
I'm going to go to my first one in September, and I was mulling over the same thing.
In this case, he only has two books out (the one he's launching and one previous) so it's not as big a deal. But I was wondering if I could take something else to be signed. Like my theatre programme. I don't mind really. I've never had a big thing about a scribble on a piece of paper - it's the face-to-face I'm excited about. I've been able to go up and speak to two of my heroes, and it meant the world to me