I am dating myself but I can remember this thoughtful tradition.
My mom was especially fond of it so she would help us create paper baskets and then we filled them with a few flowers and some "penny" treats. (and yes you could get candy for a penny!)
One year I remember putting dandelions in with some special homemade cookies.
We would then leave them on the neighbors door handle.
Now I know times are changing and the "safety" issue is a concern BUT I say
"BRING THEM BACK".
They were such a thoughtful gesture and a child's way of doing something nice for someone else.
Maybe you could have your class make one for each teacher in your school as well as the principal, secretary, playground supervisors, cafeteria workers, and custodian.
On the craft stick of the flower they could write a few kind words of thanks to that person.
I used scrapbook paper for the basket with a button on each side.
The flowers were cut from construction paper and put on craft sticks.