1Heat oven to 350°F (325°F for dark or nonstick pan). Make and bake cake as directed on box for 13x9-inch pan. Cool 10 minutes. Run knife around sides of pan to loosen cake; remove from pan to cooling rack. Cool completely, about 1 hour. For easier handling, refrigerate or freeze cake 30 to 60 minutes or until firm.
2Tint 1/3 cup frosting with yellow food color. Tint remaining frosting with blue food color. Spoon yellow frosting into resealable food-storage plastic bag or disposable pastry bag; set aside. Remove cake from freezer. Using serrated knife, cut rounded top off cake to level surface; place cake cut side down. Use toothpicks to mark sections of cake to be cut (template can be found under the Tips below); cut cake into sections.
3On tray, place largest piece. Place 1 1/2-inch strip of cake along top edge of jeans; cut off excess. Place triangles along outer edges of legs. Attach cake pieces with a small amount of blue frosting. Frost with a thin layer of blue frosting to seal in crumbs. Refrigerate or freeze 30 to 60 minutes to set frosting. Frost entire cake. Use fork or decorating comb to create fabric texture, if desired.
4To decorate cake, cut fruit snack into 8-inch length and 6-inch length. Place fruit snack on top edge of cake, overlapping in center, for belt. Cut off very small corner of yellow bag of frosting. Pipe frosting for pocket, zipper and cuff stitching. Decorate as desired with candies. Store loosely.