Boo Radley leaves Scout and Jem little gifts in the knothole of the tree. It is his way of communicating with the two children and trying to be their friend. Ultimately his friendship is made clear when he shows up in person when he saves Scout and Jem from Mr. Ewell's attack. The items that Boo Radley leaves in the knothole are as follows.
1. 2 pieces of chewing gum. Jem did make Scout spit it out, because he was suspicious.
2. 2 scrubbed and polished pennies. Jem confirmed them both to be rare Indian Head pennies from 1906 and 1900.
3. A single ball of gray twine.
4. 2 miniature carvings of Scout and Jem made out of soap.
5. An entire package of chewing gum, not just two sticks.
6. A spelling bee medal.
7. A pocket watch.