Celery salt can be one of two things.
Most commercial celery salt is a combination of salt and celery seed; but some homemade and farmer’s market salts are a combination of salt and dried celery leaves. They taste about the same, and they’re delicious, but I wouldn’t put them in tomato sauce. Because it’ll taste like the most famous tomato-and-celery-salt combination, a Bloody Mary.
From a box sold in Chicago, Illinois.
Tomato Sauce
Tomato puree–celery salt or juice and onions
Green peppers, celery and onions chopped fine. Boil in puree and remove or leave in if not too coarse.