Each person gets 42 cookies / 7 people = <<42/7=6>>6 cookies.
Each person gets 63 pieces of candy / 7 people = <<63/7=9>>9 pieces of candy.
Each person gets 21 brownies / 7 people = <<21/7=3>>3 brownies.
Each person will get 6 + 9 + 3 = <<6+9+3=18>>18 desserts.
#### 18