We used to celebrate it in only one way, we'd plant a tree every year. I used to work in a place that was upstairs from the EPA in Seattle. Every Earth Day, they would hand out millions of tree seedlings. We'd haul it to our property on the Olympic Peninsula and plant the thing on our property (7+ acres of woods) and say something like, "live or die, it's up to you now." Then we'd walk away and never look at it again. I believe they all lived as I don't remember ever pulling a dead one to the fire and I do remember where we planted them. Doug Firs like the Olympic Peninsula.
We have done anything for Earth Day since I quite that job.
Have a great one! Hug a tree today! I won't as there are likely fire ants in most of the trees here, and if not a fire ant, a nasty thorn you could use for a darning needle.