Thanks to everyone for the ideas. We performed at the library today with great success. We played seventeen songs altogether, and the following were recommended in this thread:

When the Frost is on the Punkin (Riley poem from the Anne Hills link)
On the Banks of the Wabash Far Away (state song of Indiana)
Such A Long Time, Old Friend (by Lotus Dickey)
New Harmony (by Craig Johnson)
Wabash Cannonball

I'm drained right now though. Performing takes more out of me the older I get.