The next time you pass a vending machine, tape some change or a dollar bill to the side of the vending machine with a note saying “Your snack’s on me!”
If you don’t have tape on hand, leave the change in the change dispenser at the bottom of the machine with a similar note. You will make someone’s day!
Encourage the recipient to pass on their good fortune and leave their change for the next person. Or commit to doing this act once a week at various vending machines. You could also do this with parking meters!