ubiquitin: Here was the initial question: “What family traditions did you grow up with that you thought were just yours and later found out were not so uncommon?”
In the shul where I grew up (1960’s and 1970’s), most people made the brocha on lulav and esrog in shul right before Hallel. They did not go down to the shul’s sukkah. So in my neighborhood it was not “common” and only later did I find out how common it was.
Eating an egg at the seder is not universal. Again, in my neighborhood it was not common.