He eats 2 each from Monday through Friday for a total of 2*5 = <<2*5=10>>10 candies
He eats 1 each every other day of the week (Saturday and Sunday) for a total of 1*2 = <<1*2=2>>2 candies
In a week, he consumes a total of 10+2 = <<10+2=12>>12 candies
Doing this for 3 weeks, he will consume 3*12 = <<3*12=36>>36 candies
If 2 packets contain 36 candies, then 1 contains 36/2 = 18 candies
#### 18