Well, we celebrate what we
will be doing - going on "voyages" of discovery.
We go to a river or stream early in the morning (on the day after Labor Day). We sit on the bank, eat breakfast on a blanket and make
paper boats. Then we "launch" them very ceremoniously with speeches about the voyages to the lands of Geometry, Rome, Reading - or whatever we have decided to learn about that fall.
Then we just play for a while.
One year, we were by a calm river and the boats just floated out of sight. Then we moved to a place where the only launch site was really a pond with a streamlet. I was so concerned about how the kids would respond to seeing their boats sink eventually, but it didn't bother them, it became quite a game to play in the streamlet, and they always ended up IN the water and swimming. But still, if the child is very young, perhaps leave shortly after the launch. The older kids "get" the ceremonial nature of the launch.
I got this idea from a mom on the Waldorf discussion list several years ago - they did it at the beach!
Best wishes,
Lucie
P.S. I guess I don't feel the need to celebrate not going to school since my kids have never been in school.