How Come At Celebrity Book Signings, They Won't Allow You To Have Other Things Signed?

The stars are there to sell their books and not everything else or they would never get through the lines of people. Sometimes you can try to purchase an item earlier than the day of the signing and just have it on your person. Then when you get YOUR book signed ask them if they would also sign that. Once you are up there no one can do anything about it so its worth a try but it will still depend on the signer to do or not to do it.