An interesting question. In part this would depend on what Scout means to you, and what you want to remember about her. In part, though, you would put things to represent those things that are most Scout, or that relate to her most important experiences. For example, one of my favorite scenes is when she visits Calpurnia's church, but what would represent that?
In general, though, I'd put a picture of Hitler (because of the role in the argument), something to represent a courtroom (because the trial was so important to her), ashes (for the burned house), letters (related to reading), some foul language (to represent her wonderful cursing), and something to represent the relationship with Boo (and her costume).