Simple thing can be so meaningful if they come from the heart. I used to write quotes or messages on the free newspaper you could get in the train stations and then leave it on a train for someone to find.
A stranger paid my bill once and it was the most unexpected moment and the joy I felt from it was unsurmountable. I was so grateful for this random act of kindness that I really want to return the favor to someone else who is deserving. Pay it forward!