To make brownies:
Preheat oven to 350 degrees (175 degrees C) and grease an 8-inch or 9-inch square pan. Place dry brownie mix in a large bowl. Add 1/2 cup vegetable oil, 2 eggs, and 1 teaspoon vanilla extract; stir just until combined. Pour into baking pan and smooth the top. Bake until a toothpick inserted into the center comes out clean, 20 to 22 minutes. Allow to cool before cutting into squares.
Having pre-made plastic bags of this brownie mix allows you to scale the recipe as needed. It's easily doubled, quadrupled, etc.