In an extra large bowl combine cabbage, carrot, and green onions. (If desired, use 24 cups of purchased coleslaw mix in place of the cabbage and carrots.)
For dressing, stir together mayonnaise, sugar, vinegar, celery seed, and salt. Just before serving, pour the dressing over the cabbage mixture; toss to coat. Makes 25 side-dish servings (about 15 cups).