Step 1: Collect Supplies and Measure
1 Bag that needs interior pockets
1 sheet of 12"x18" 7-mesh plastic canvas
1/2 yard of fabric; I used 2 flat quarters
1/4 yard stiff interfacing; I didn't use fusible web, but you could
Devices to put into pockets
Paper and pencil to take notes in
Snacks, in case you get hungry
Step 2: Cut Fabric and Sew the Pocket Strip.
Fold the second piece of fabric, the pocket fabric so that, when folded flat, the folded area is 1" shorter than your chosen devices. Cut this piece out - making it at least 5" longer than the backing piece. In my case, this was about 3" tall and 22" wide.
Cut one piece of interfacing the same size as the pocket piece. If you're using fusible web, iron it on to the wrong side of the pocket piece.
Place the interfacing on top of the folded pocket strip. Sew one of the short sides of the strip and the long side. Turn the pocket strip right side out and iron flat.
Step 3: Fit Pocket Strip to Backing. Sew Pocket Strip Down.
Carefully, sew the pocket strip to the backing. Sew along each pin-marked pocket line, removing the pins so your machine doesn't get damaged.
Sew down one short side, taking out the pin before your sewing machine hits it. Then, turn and sew along the long edge, easing the wrinkles and extra fabric of the pocket strip into the shorter length of the backing. Larger devices (like my camera and wallet) will require taking folds in the pocket fabric. Sew up the second short side, removing that pin as well.
Step 4: Sew Backing Together
Measure the plastic canvas and cut it slightly smaller than the backing fabric. Cut very close to the "line", so that no little tabs stick out. If, like me, you're making a bag filler that has a bend in it, cut the plastic canvas into parts - measure the smaller part of the bag filler and cut the plastic canvas small enough to fit in each section.
Insert the plastic canvas into the tube of the backing fabric.
Sew along the line of the fold in the bag filler (again, if you're making one that bends).
Step 5: Sew Backing Closed. Insert in Bag!
Once the liner is done, check one last time for fit and put your new pockets in your bag!
Enjoy the feeling of having a bag you can actually keep everything you want in!