My friend picked up these cool old Royal Mail bags, and wanted me to turn them into a messenger bag. They were too two-dimensional to fit his laptop and various sundries, so he wanted me to put the two of them together. This was my solution. It's really durable, and I think it looks pretty good!

Note: I sewed this in a kind of stupid order, but I put the steps in a better order. So don't get confused if my photos show things that are sewn that I haven't mentioned sewing yet. Just follow the directions.

Step 1: Materials

You need:
Two Royal Mail bags (mine were different sizes and designs)
3 72" long pieces of 3/4" webbing
3 buckles & rubber O-rings
A formidably tough sewing machine
scissors

Step 2: Remove Plastic Bit

From the darker orange (larger, thicker) bag, remove the green plastic tab.
This is somewhat difficult.
A hammer does the trick.

Step 3: Ripping Apart

Take apart the side seams of the dark orange bag.
Also remove the black plastic/leather piece from the front of the light orange bag.

Step 4: Cutting Bits

From the light orange bag, cut:
3 4" wide strips from the back, one as long as the bottom of the dark orange bag, and the other two as long as the dark orange bag's sides. (You can substitute one of the shorter
Cut out the clear pocket from the front of the light orange bag.
Cut out the zipper from the light orange bag, keeping as much fabric attached as possible on the top and bottom.

Step 5: Patching

Patch any holes with scraps of fabric from the light orange bag.

Step 6: Padding the Bottom

Cut the black plastic/leather piece in half.
Sew the halves onto the long orange strip at the ends.
Tip: pins don't work very well in this thick fabric. I recommend rolling up some duct tape and sticking it on to hold pieces in place.

Step 7: Side Pocket

Hem the edges of the clear plastic pocket.
Sew it onto your most plain short orange strip. Leave the top open so that there's a clear pocket built in, and a larger opaque pocket behind it.

Step 8: The Strap

At this point, you should have three strips of webbing, each 72" long. 72 inches might be overkill, but it's a good length to start with.

Singe the ends with fire to seal them.

Stitch the pieces of webbing together, side by side, at either end, to make one wider strip (only for about a foot at either end). Here's how: place the strips of webbing side by side. Set your sewing machine to a wide zigzag stitch. Sew straight down the middle between the two strips of webbing, and they should become joined.

Sew the two ends of the straps to the back panel of the dark orange bag. Try it on to make sure that the strap will not be twisted when you're wearing it.

Measure about 24" up from the side of the straps that will be forward when you are wearing it. Cut straps straight across, and again use fire on them. Affix the buckles as shown in the pictures. Make sure to try it on while you are figuring out the buckles!

Step 9: Sewing Together

Sew the bag together. Use parallel double stitching for durability.

Right sides together:
Sew the bottom panel to the side panels.
Sew the bottom panel to the front and back panels.

Right side out:
Topstitch zipper into place. The zipper should be a little too short; sew in a patch of excess fabric as shown.

Inside out:
Sew the sides to the front and back panels, up to the decorative zipper.
Sew sides to top, straight across. This should be an angled seam, forcing you to trim triangles from the side panels.

Turn the bag right side out.