Heat oven to 350°F Grease bottom only of 13 x 9 x 2-inch pan.
Beat cake mix, water, oil, and egg whites in large bowl with electric mixer on low speed for 30 seconds; move to medium speed for 2 minutes. Reserve 1 cup of batter.
To the reserved batter, add the allspice and cinnamon; stir and set aside. Pour remaining batter into pan.
Drop the reserved batter by tablespoons all around the batter in the pan (about 12 to 14 mounds); swirl the batter together in an “S” shape.
Bake 28 to 33 minutes or until toothpick inserted in center comes out clean. Cool completely for 1 hour. After cake is cooled, make frosting.
Beat all the ingredients of the frosting together in a chilled bowl until soft peaks form. Frost the cake. Just before serving, sprinkle each piece with crushed root beer candies. Store covered in refrigerator.