Chocolate Walnut Snack Cake

1 1/2 cups all-purpose flour
1 cup sugar
1/4 cup cocoa
1 tsp baking soda
1 tsp vanilla
1 T white vinegar
1/4 cup vegetable oil
1 cup cold water
1/4 cup chocolate chips
1/4 cup chopped walnuts

Preheat oven to 350°. In an ungreased 8-inch square baking pan mix first four ingredients with a fork. Stir in remaining ingredients except for chocolate chips and walnuts and mix well. Sprinkle chocolate chips and walnuts over batter. Bake for 30 minutes or until done (when knife or wooden pick inserted in center of cake comes out clean).