Hemma Design Sonja Backpack to Bag Pattern Hemma Design Sonja Backpack to Bag Pattern. A little lined backpack that will convert to a cross-body bag depending on your need. All it takes is a re-tying of the shoulder straps! Choose from a foundation pieced or color-blocked option. Finished size about 10 1/4 x 11 x 4 1/2 without gussets. Includes instructions, diagrams, and tissue paper patterns.