Sounds like fun! Think about things—artifacts, words/quotes, events, people, etc.—that relate to Jem in the story. First of all, by the end of the book, Jem has grown significantly. The items on your memory box could represent the maturation of Jem. Perhaps you can make a creative timeline of Jem’s life and wrap symbols around the outside of the box.
I think some “must haves” would probably be symbols you’ve already thought of—the mockingbird, the items left in the tree, and perhaps part of the cast from his broken arm.
Think about what Jem associates with each character and the events. For example,
- If Jem had one keepsake of Atticus’, what would it be? His closing statement in the trial? His gun?
- What photographs would he have saved? Dill hiding under the bed? Scout rolling in the tire? The rabid dog?
- What places were important to him? Perhaps he has a chip of paint from the Radley house or a “poisonous” pecan from the Radley tree.
- What would symbolize Calpurnia’s influence on Jem? A Bible? An apron?
- What are some cherished items he has? The air rifles? A script from the Boo Radley plays?
- Mrs. Dubose? Mr. Avery? How could you represent their influence?
All this project takes is a little insight into Jem as a character and a little creativity. Think back to the episodes throughout the book and come up with things that show not only the sentimental side of Jem but also the hardships he went through.