Many songs can be played with just these two chords.

The chain gang chant "Long John" for example.
Also, you could just use these two chords on "This Little Light Of Mine".
"I'm Gonna' Sit at the Welcome Table". Other spirituals come to mind.

I minor to IV major (highlighting a "Dorian" mode) can be used on "Follow the Drinking
Gourd"....you could ignore the V minor or bVII chord here.

There are many songs that could just use these two chords by-passing the V chord.

Not sure how interesting they would be harmonically, though.