Slice the ends off the green onion, and then slice thinly. I use the entire onion - white and green parts.
In a large bowl, combine the slaw mix and the onion.
Add the cider vinegar and 1/4 cup of Mayo. Sprinkle the Celery Salt on top of the mayo.
Using a large fork, stir to combine. Mix thoroughly, and add additional mayo if a creamier sauce is desired.
Refrigerate at least 30 minutes before serving.