Preheat your oven to 325°F (163°C).
In a large bowl, mix the dry ingredients: cake mix, flour, sugar, salt, cinnamon, and baking soda.
In another bowl, whisk together the wet ingredients: eggs, oil, sour cream, milk, and vanilla extract.
Gradually combine the wet ingredients with the dry ingredients until just mixed.
Fold in the grated carrots, crushed pineapple, shredded coconut, and pecans (if using).
Pour the batter into greased cake pans.
Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.
Frost with cream cheese frosting once cooled.