First, I want you to grab something to mark with. I prefer disappearing fabric markers, but chalk or even a quilter's pencil will work too. On the wrong sides of both the lining and the exterior pieces, I want you to draw a line 1/4 inch in along the top and bottom edges (where the zipper will go), and also on the short edges of those flaps that extend. It can get a wee bit fiddly, and I find this step to go much more smoothly if I have a guideline to follow.
You should have eight lines drawn per piece--two long, and six quite short. Once you have this done, you'll make a sandwich. I'm talking about a zipper sandwich, but if you're hungry by all means take a break. Take your exterior piece and place it face up. Place your zipper face down on top of that. The zipper I told you to use will be too long, which is fine. It makes it much easier to sew in. I always use zips that are too long as I'd rather trim than spend too much time tinkering with everything and breaking needles on metal bits. OK, so exterior is face up, zipper is face down, and lining is face down. Pin those layers together.
I use a quarter inch presser foot for this part and am really pleased with the results, but if I didn't use that I'd be using a standard foot with a 1/4 inch seam allowance. I almost never use my zipper foot. This part is very important so pay attention to what you're doing. You're going to stitch these layers together following that long purple line that you drew, BUT you need to start and stop 1/4 inch in from the edges. One of the short lines you drew should intersect, and that point will be where you want to start and stop sewing.
That purple line is exactly where I'm starting my stitch line...
...and ending my stitch line.
Arrange everything right side out, and use a pressing cloth or finger press that seam a little bit. Then, starting and stopping exactly where you did when installing the zipper, top-stitch. The seam will be a little bulky, so the topstitching will help keep everything in check.
You can very faintly see my purple mark and how I've left that teeny bit loose at the end.
Repeat for the other side of the zipper--exterior face up, zipper face down, lining face down, pin along the top. It will look like this just before you sew:
Stitch in the same manner as before, making sure to indent your stitching at each edge. Same with the topstitching. This is the part where you'll appreciate the extra zipper length. That wee bit extra makes it easier to maneuver around the ends of the zipper. Once you're all topstitched, you're going to want to unzip, and then pull exterior and lining away from each other so they look like this:
Then turn that whole thing inside out. Zip your zipper closed a little, maybe just less than halfway? You want to make sure your pull isn't going to get sewn outside of your seam, but that it's open enough for turning later.
Arrange your layers like this:
They're stacked on top of each other, and the zipper is running right down the center. We're going to stitch the lining first. You'll have two flaps of your lining extending off each end, one attached to the zipper, and the other solid. Line those up and pin your short edges together:
Sew along that 1/4 inch line you made from end to end, pulling the exterior fabric out of the way of your presser foot as you go. You can leave the zipper laying flat and sew right on over it.
Repeat for the other side. Now we're going to do the same thing with your exterior, but before you pin, grab your zipper tabs. Insert one between the two exterior layers, centered with the zipper. The tab will be tucked inside, and the raw edges poking out a little.
Again, sew long the line that you drew, pulling the lining out of the way As we've already stitched that, it may kick up a little fuss as you try to move it out of the way--
When it does that I do my best to get it out of the way, but it's not too concerning if you stitch over it a little bit. As a matter of fact, here's a second option for you for this part if you find the above too frustrating. Sew along your guideline until you get to the zipper tape, backstitch, clip your threads. Then move your piece ahead just to the other side of the zipper tape and sew the rest of the seam. Then lay all those layers on top of each other--the lining and the exterior. You'll want to put the exterior on top so you can see the little gap where you stopped stitching. Now go back and sew that spot going through all the layers. It should look just fine when you turn it right side out. It's essentially the same as if you accidentally stitched through your lining as it got in your way, but it's less frustrating than trying to fight that fight and won't get you any unintended folds in your fabric.
Repeat for the other side. Don't forget to insert your other zipper tab!
OK, now we've got a big weird piece of thing. All we need to do is sew those gaps on the sides closed and we're finito benito.
Red and blue makes a happy side seam! It also makes purple, but that's beside the point. Essentially, the edges 'marked' by the red and blue lines come together, and we've got a boxy side seam. And we need to do it many times (eight edges between inside and out, remember). So pick one to start with. Get the top and bottom corners pinned in place, then pin the rest of the seam. Everything should line up nice and even, but if it's a little bit off just ease it in and you'll never notice. Stitch.
Do this four times for the exterior and three for the lining as we need to leave a gap in one for turning. I'd recommend that you sew up the edges with the pleated pocket first, as those edges can be machine sewn in nice and tight. If you leave one of those edges as your gap, it'll a little bit annoying to sew shut from the outside while keeping the pocket neat. I like to line up the pocket edge with the side of the bag and pin, then pin the edges together and sew.
You can see here before I pin this side shut that I've pinned the pocket in place so I'm sure to stitch it into the seam.
Once you've done that, carefully reach through the gap in the lining and through your zipper that you left open. If you didn't open your zipper you might be cursing yourself now, but the fix isn't impossible. Simply pick out the seam of one of the exterior sides you just sewed, reach in, open the zipper, and close your seam back up. But if you did leave it open, carefully pull everything through and out of the gap in the lining until everything is right side out.
If you reach through the gap in the lining, you can get your hand into the exterior section of the bag and get your corners poked out nice and neat. Once you've done that, turn in the raw edges of the lining gap, and pin. Then you can either stitch shut by hand or by machine. Tuck the lining down into the bag.
We need a final press to get rid of the wrinkles from all that turning and twisting. A bag like this can be a bit difficult to get your iron into except along the edges where the zipper is. So I like to stuff a few dishtowels in there, zip it shut, and press away. I let it sit for a few minutes and then remove the towels, leaving myself with a nice neat bag.
And that's it!! Hopefully you've learned a few things along the way. I know that I gave you a LOT of information here, but trust me, once you make one any more that follow will be much easier as you'll be familiar with the technique, and may just need to check measurements and placement. I know I'm super excited to use mine for my toiletries and makeup when I travel. It'll be so much nicer than my current multiple ziploc bags method (I know, I should be ashamed of myself).
So let's review:
Insanely sturdy handles? Check.
Delightfully pocketed lining? Check.
Zipper and pull tab? Check. Ribbon on your zipper? Optional check.
A project you can be proud of? Hoping that's a check :)
As always, I do not mind if you sell things made from this tutorial. I'd actually be pretty flattered. I do ask, as this has taken me an incredibly long time to sew, photograph, write, and edit, that you do not distribute this pattern, rewrite it, and/or claim it as your own.
I have done my mind-numbing best to make things as accurate and as clear as possible, but I'm human and we all know what that means. If you've got any questions, please let me know in the comments and I'll do my best to clarify.