You could applique the state bird of each state you touch.
You could applique the state flower of each state you touch.
You could applique the state flag of each state you touch.
You could make your own pattern with each block with the state
bird, flower and flag on each state you visit.
Or find a pattern in each state that stands for something historical there. This sounds like you will wind up with a real treasure that you and your DH will now and then point to one block and say "Do you remember when you and I went....?"