In To Kill a Mockingbird what gifts are given in the knot-hole of the tree and what might they reveal in the unfolding of the plot?

At this point in the plot of Harper Lee's To Kill a
Mockingbird, Scout is now in the first grade. This means that she gets out 30 minutes
earlier than Jem and has to walk home alone past the frightening Radley property. One
day while walking home, she sees something shiny in the knot-hole of one of the huge oak
trees on the Radley property. The shine is coming from the wrapping around two pieces of
gum. On the last day of school, inside the know-hole of the tree Jem and Scout find a
box covered in gum wrappers and inside the box are two Indian-head
pennies.

What those gifts reveal is that somebody is aware
of their presence and has been watching them. That somebody is Boo Radley himself. This
is an attempt on his part to make contact with the kids and have some sort of
communication with them.