Use a 1⁄2" seam allowance unless otherwise stated.Place 12×30-1⁄2" batting rectangle on flat surface. With right sides together, layer green print and blue denim 12×30-1⁄2" rectangles on top of batting; pin. Sew around outer edges through all layers, leaving a 6" opening along center of one short end for turning and the button loop (photo 1).
Do not sew over pins. Stop stitching and remove pins right before the needle gets to them (photo 2).
Trim across corners and trim seam allowance to 1⁄4". Turn layered rectangles right side out through opening and press. Fold in opening 1⁄2"; press (photo 3).
TIP: Use a chopstick or the eraser end of a pencil to push out corners.
Fold the green print 1-1⁄2×5" strip in half, wrong side inside. Press, then unfold. Fold long edges in to meet at the center; press again. Fold in half, matching folded edges. Topstitch 1⁄8" from long edges to make a button loop (photo 4).
Fold button loop in half and place in opening of layered rectangles at center of short edge, with raw ends inside opening; pin. Topstitch around entire rectangle 1⁄8" from all edges (photo 5).
Fold and press a blue denim 2-1⁄4×24" strip in half lengthwise. Open pressed piece and place a 5⁄8×24" batting strip along folded edge. Refold, matching long edges; pin. Machine-zigzag-stitch around three edges to make one strap. Repeat to make a second strap (photo 6).
TIP: Ask for help setting the sewing machine to a zigzag stitch. If your denim frays, clip away stray threads and make a second row of zigzag stitches over the first. Or make a smaller zigzag stitch.
Place one end of a strap on green print side of layered rectangles 4" down from button loop and 1-1⁄2" from side edge (Diagram 1). Machine-zigzag-stitch in place. Measure down 9" from just-sewn top of strap and sew bottom of strap in place. Repeat with remaining strap on opposite side (step 7).
Using blue denim 2-1⁄4×9-1⁄2" strip and 5⁄8×9-1⁄2" batting strip, repeat Step 6 to make a handle. Place one end of handle next to top of a strap, with short side of handle perpendicular to strap. Machine-zigzag-stitch in place. Repeat with opposite side to attach handle (photo 8).
Fold and press the blue denim 7" square 5⁄8" from one edge. Topstitch folded edge using a straight stitch. Fold over remaining edges 1⁄4" and press (photo 9).
TIP: It helps if an extra pair of hands holds the fabric straight while you press.
Center pressed square on green print side of layered rectangles with topstitched edge 4" from edge; pin (Diagram 2). Topstitch 1⁄8" from three folded edges to make pocket (step 10).
Fold layered rectangle, blue denim inside, with button-loop end 4" longer; pin. Topstitch 1⁄2" from side edges.
TIP: Backstitch at beginning and ending of seams to secure (photo 11).
Hand-sew button to front to complete backpack (photo 12).