There are 8 ounces of cereal left in the box.
Dena ate 1/6 of the cereal, leaving 5/6 of the box for Joey.
Joey then ate 2/3 of the box, which is equivalent to (2/3) × (5/6) = 10/18 of the box.
The amount of cereal left in the box is therefore 18 - 10 = 8 ounces.
Therefore, there are 8 ounces of cereal left in the box.