1Heat oven to 350°F (325°F for dark or nonstick pans). Grease bottoms only of one 8-inch or 9-inch round pan and one 8-inch square pan.
2In large bowl, beat cake mix, soda pop, oil, egg whites and a few drops food color with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Divide batter evenly between pans.
3Bake 26 to 34 minutes or until toothpick inserted in center comes out clean (times may vary between the two pans). Cool 10 minutes. Run knife around sides of pans to loosen cakes; remove from pans to cooling rack. Cool completely, about 1 hour. Freeze cakes uncovered about 1 hour for easier frosting if desired.
4Place round cake near one end of tray for globe of gum ball machine; frost top and side with half of the frosting. Place square cake next to round cake for machine base. Stir 1 teaspoon food color into remaining frosting; frost sides and top of base with frosting. Wrap candy bar with foil. Place foil-wrapped candy bar near bottom of base. Use decorating gel to draw trap door on candy bar. Arrange chocolate coin and peanut candy above candy bar. Arrange gum balls on globe. Store loosely covered.