There are so many symbolic elements of this classic novel by Harper Lee.
You might start by considering bringing something into class that relates to the items that Scout and Jem found in the old tree by their house. These items include some chewing gum, an old stopwatch, and a two shiny coins, and the tree serves as a valuable conduit of communication between child and their unseen playmate in Boo Radley throughout much of the novel's first act. The fact that the items are left in the tree throughout much of the children's non-interaction with Boo Radley symbolizes the fact that the mysterious next door neighbor is, as his name suggests, almost something of a ghost; never fully seen, but never fully absent.
Other items of symbolic importance would include some sort of replica of the eponymous mockingbird to which the title alludes. The novel is loaded with themes of imprisonment and escape, and the mockingbird -- as Atticus tells Scout -- is symbolic of a creature that is guiltless and deserving of a free and unfettered existence. Mockingbirds do nothing to harm anyone, choosing instead to spend their days singing songs for all to hear. Accordingly, "it is a sin to kill a mockingbird," and in many ways, the mockingbird is a metaphor for all creatures who are "cooped in" and persecuted by those around them in spite of their having done nothing but good in return. Many critics suggest that both Tom Robinson and Atticus Finch are, in their own respective fashions, "mockingbirds" of the post-Reconstruction era South in which the story is set.
You might also consider some symbols for your class to associate with the story: a bird cage, a gavel, a first-grade reader, a page of stock market quotations, a pair of scisors, a piece of chain. . . You might wven find a tree branch with a significant hole in it-- not as large, of course, as the tree trunk, but representing the idea of the hollow tree.
Some might serve as mnemonic devices to help recall incidents in the story. The class might discuss how the objects relate to themes in the story and thus become symbols.