Preheat oven to 375 degrees. Line a 11-inch by 17-inch or larger baking sheet with parchment paper or aluminum foil.
Unroll crescent roll triangles and arrange into rectangles to from a crust, pressing the seams together.
Bake the crust according to the package instructions, about 12 to 15 minutes or until golden brown. Remove from oven and cool completely, at least 30 minutes.
Meanwhile, in a medium bowl, combine cream cheese, mayonnaise, and ranch dressing mix. Chill in refrigerator to blend flavors while crust cools.
Spread the cream cheese mixture over the cooled crust. Top with broccoli, cauliflower, and carrots. Sprinkle with cheese and any additional vegetables, if using. Chill before cutting into squares.