Of Promises & Paper Airplanes has a specific scenario and motif — one of the Characters is on their way to the airport while the other one is folding a paper airplane. 

The Supplement provides more options so the Guide can choose a different scenario (The Meeting Place) and motif (The Task). 

Here are some examples: 

• Of Promises and Photographs, where the Characters and the player/s take a photo after each Encounter.
  
• Of Promises and Paintings, where the Characters and the player/s draw or paint after each Encounter.
• Of Promises and Poetry, where the Characters and the player/s write or recite a verse or poem after each Encounter.

It doesn't have to be an alliteration either. The Guide is free to change the scenario and motif to better fit the story. 

The Supplement also features a simplified Timeline and two additional options for the Time Skip (Short-Term and Long-Term). 

Enjoy!