What do Jem and Scout think of the things they find in the knot hole of the tree in To Kill a Mockingbird?

The first thing that one of them finds is chewing gum. 
Scout finds it and chews it and Jem gets all angry at her.  But then they keep finding
more stuff.

At that point, the two of them talk about it a
bunch.  They decide that the knot hole must be someone's secret hiding place.  So they
think that someone must have put the stuff there because it was valuable to
them.

So they decide to hold on to the stuff and wait until
school starts.  At that point they'll see if it belongs to
anyone.

You can find this in Chapter
4.