I will show you how to make a 3-pocket travel bag that you can carry your charging cables, battery pack, and/or USB sticks. Here's what you need:

sewing machine
fabric of your choice (I prefer cotton canvas because you can buy 60 ft wide by 1 yd length between $7 and $10 at Blick's Art Supplies)
seam ripper (for any mistakes)
Three zippers
Screen Printing Ink (optional)

The measurements of the front pockets are 4 inches (bottom), 1.5 inches (middle) and 8 inches (back pocket).

Step 1: Cutting the Fabric

First use a few sheets of paper to get an idea on how the bag layout will be.

For this project, I've added an extra inch on my fabric in case the pieces are not the same width. It can be trimmed later on.

Cutting the fabric:

1 - 5 inches x (length of zipper + 1 inch) - bottom section
1 - 2.5 inches x (length of zipper + 1 inch) - middle section
1 - 3.5 inches x (length of zipper + 1 inch) - top section
2 - 9 inches x (length of zipper + 1 inch) - middle layer and back layer

Step 2: Sewing

Note: For extra durability, I sewed all areas twice.

Sewing the sections:

Take the bottom section sheet of fabric and fold an half inch down. Use masking tape / painter's tape / pins to hold the folded layer down. To make it easier, use a cutting mat and use a ruler with a pencil to mark the location.
Use an iron and iron the fold. This will make a crease. This helps with sewing the zipper on and prevents the exposure of frayed fibers.
Using the front side of the zipper, align the edge of the zipper to the edge of the 1/2 inch fold. Secure it with pins or tape.
Unfold the crease with the zipper attached can carefully sew close to the zipper as possible without hitting the teeth.
Repeat the steps again with the middle section. This time align the creased edge to the other half of the first zipper. Unfold the middle section and sew.

You should now have the following sewed together:

Bottom section
1st zipper
Middle section

The next few steps are going to be repetitive again as you sew the second zipper and top section.

Once you've sewn on the first half of 3rd zipper, continue to optional silk screening portion. If not, please read below.

Continuing with the 3rd zipper, sew the back layer to the other half of the 3rd zipper using the steps above.

Now here's what is currently sewn together:

Bottom section
1st zipper
Middle section
2nd zipper
Top section
3rd zipper
Back layer

Middle layer

Flip everything over revealing the back side with all the stitches.
Take the middle layer and align it with all sections (see picture).
Mark a 1/4 inch from the top of the middle layer and sew it to the top zipper. Make sure the edge is not close to zipper. Otherwise the zipper will get caught in the fabric.
Once the middle layer is secured, trim the extra amount of fabric.
If your sewing machine has a zig-zag stitch, change to that setting and sew the sides of the middle layer and the bottom layer (the zig zag stitch prevents fraying of the fibers)

Creating the bottom and middel pockets

Flip over to the front side.
Starting with the bottom pocket, sew above the bottom zipper. There should be a stitching from earlier on when you sewed on the zipper. You can use that as a guide and sew over it so that you don't see multiple stitchings.
Do that for the middle zipper too. (Please see image). The pocket may be too small to fit some items. If you need the extra space, don't sew there. You will then have the spaces from the middle and top sections.

Creating the back pocket

Take the back layer and fold it over the front, which will cover the middle and bottom zippers. (see picture)
Align the sides and bottom. Use the zig-zag stitch and sew the sides and bottom. Trim any excess fabric.
Carefully open the top zipper all the way and carefully invert it.
Once everything is invert, carefully push the corners from the inside to form the corners of the bag.

Congratulations you now have completed the bag!

Step 3: Screening Printing (optional)

I'm using water-based screen printing ink so that I can let the ink air-dry. I don't have screen printing oven to dry the ink.

Screening printing

Make sure you didn't sew on the back layer yet.
Grab an image you want to place on the blank area of the bag.
Use a vinyl cutter (Silhouette Cameo or Cricut are inexpensive multi-stationery cutters) and cut out your image on a sheet of vinyl which is the same size as your back layer.
Place the back layer on a flat surface and transfer the cut out image on vinyl over the back layer.
Make sure there are no air pockets when you transfer the vinyl on the back layer. Having air pockets will cause the silk screen ink to bleed on the fabric distorting the image.
Apply painter's tape on all sides without covering the image.
Put the screen over the image and again, put painter's tape on all sides.
Put some screen printing ink across the top of your image.
Use a screen printing squeegee and pull the ink over the image. Make sure you cover the entire image. Do three passes to ensure enough ink comes through the screen to cover the entire image.
Once you covered the entire image, remove the screen and let it air dry.
Once the ink has dried, peel off all the vinyl and you should now see your image printed on the fabric.

Congratulations on screen printing an image! Please refer to the steps on sewing on the back layer.

Tip: When sewing on the back layer with an image, the image should be facing the top and the back layer should be folded over covering the zippers (see picture).