To celebrate May 1st as a child, my friends and I would create paper baskets...construction paper rolled into a cone shape and filled with flowers. Then we would go up to our neighbors doors, hang the "basket of flowers" on their doorknob, knock and then run and hide.
It was thrilling to watch them find the flowers and look around to discover the giver.
Now I realize those were my first experiences in giving anonymously. It was pure pleasure and still is.
Amy Krouse Rosenthal describes the same thrill in her book "Encyclopedia of an Ordinary Life". She suggests leaving spare change somewhere for someone to find. She adds a note telling them to take it if they need it and then to do the same for someone else someday.