Many women use different bags every day and it's a big problem to transfer the stuff between bags. Bag organizer is a great idea to handle this mess. And you can do one of them if you have the following materials and tools:

100cm x 150cm Fuchsia cotton fabric (Or any color you want)
50cm x 150cm Blue cotton fabric (Or any color you want)
20cm x 150cm Fabric with flower pattern (Or any pattern you want)
1 Magnetic snap
Sewing thread
Scissors
Ruler
Sewing machine

Step 1: Cutting the Fabric

For the main body, cut 2 pieces of Fuchsia fabric each measured 20cm x 28cm
For the interior, cut 2 pieces of blue fabric each measured 20cm x 28cm
For the pockets, cut 2 pieces of Fuchsia fabric each measured 15cm x 28cm
For the snap holder, cut one piece of 6cm x 13cm Fuchsia fabric
And cut 2 pieces of patterned fabric each measured 7cm x 28 cm

Step 2: Sewing the Pockets

Sew the 7cm x 28cm patterned fabric on the 15cm x 28cm Fuchsia fabric. To create a clean look, sew the fabrics on the reverse and then flip the fabric inside out. After flipping, sew the bottom line of the piece. Do one more of this. These will be the pocket pieces.

Put the pocket piece on the 20cm x 28cm Fuchsia fabric and attach it with some needles. Now draw the lines whereever you want to add divisions. As you can see, I preferred to have two divisions on one side and three on the other. Finish the pockets by sewing on the lines you draw.

Step 3: Put the Body Parts Together

Put the two pieces on each other (the pockets are inside) and pin with needles. Now just sew three edges to create the main body. When you flip inside out, you'll see that the bag is nearly over.

Step 4: Lock With the Magnetic Snap

Attach one piece of the magnetic snap to the 6cm x 13cm fabric, and the other piece on the bag itself. Fold the fabric and sew every edges. This will be the lock of the main division.

Step 5: Inner Coating and Putting Together

Put the blue fabrics on each other, pin them with needles and sew three edges. This will be the inner coating of the bag.
Now put the strip with the magnetic snap and the inner coating inside the bag. Pictures would tell you more.
Sew the mouth of the bag to bring every part together(main body, inner coating and the strip).