Shell fabric: 8" wide x 18" high
Lining fabric: 8" wide x 18" high
Velcro: 6.5" loop piece and 6.5" hook piece. I'm using self-sticking because it's what I had. I don't recommend it because it's not sticky enough to hold without stitching and when you stitch through it your needle will get sticky. This will cause your bobbin to become sad and tangle your thread and make you cry. I don't want you to cry. If you're making just one of these you can maybe get away with sewing self-stick. More than one? Forget about it or be willing to change your needle multiple times. (<--- bitter voice of experience)
A note on fabric selection. For the shell fabric cotton works great. I was making this bag to replace Eric's first lunch bag. He's a very good boy and takes his lunch every day and he wore out his first bag after about a year of use. He also loves the Cowboys and since he is such a good boy and they had a piece at the cheapy fabric store he is rewarded. Logo is copyright NFL, please don't report me or sue me.
For the lining you can choose cotton again or something that is a little more waterproof. Some people use organic cotton since you will be packing food in this bag. Others chose PUL (the stuff reusable diapers are made from) because it's so waterproof. I like ripstop nylon because it's a little bit waterproof but doesn't have polyurethane like PUL. You can get ripstop nylon in the fabric store with the sporting/outdoor fabrics.
Step 1: Attach Lining to Shell
With right sides together, sew lining and shell fabric along shorter side (8" in our example) using a 3/8" seam allowance.,.
Turn right side out. Press to align seams. If you're using something other than a cotton lining, press from the shell side to avoid melting the nylon or PUL. You should now have this. Long edges are still unfinished. If you're using nylon it might slip a little bit. Unless you had a lot of slip, don't worry about it. I put some fudge in the seam allowances to allow for this.
Step 2: Attach Velcro
Align one piece of velcro, hook/loop side out, on the right side of the lining fabric so it is centered on the short edge and with the top edge about 1/4" from the seam you just sewed. The distance from the top is mostly aesthetic, but I found this to be a nice margin. Stitch around all four sides to make sure it's nice and secure. Repeat for the other short edge.
Step 3: French Seam, Part Un
Fold the bag so the lining sides are together (i.e. shell side out). You may want to attach the velcro to make sure everything lines up nice and pretty. We're going to secure this with a french seam because it's pretty and fancy and will keep les crumbs from collecting in the seams.
Lining sides together (shell side out) stitch the sides together using a 1/4" seam allowance.
Notice we still have a raw edge on the right side of the fabric (also notice the ugly tangled stitch from my sad bobbin. I fixed it after this picture :). Trim this to 1/8". If we were making a garment now would be to the time to do some more pressing, but it's not really necessary. If you do press, press the seam to one side not open. Now to finish the french seam.
Step 4: French Seam, Part Deux
Turn your bag inside out so the shell sides are facing and the lining is out. Sew the same sides together again, this time using a 3/8" seam allowance. You will be enclosing the raw edge of the first seam inside this seam.
The inside seam will be sealed now, which will keep things nice and tidy inside the bag. Voila.
Ta-da! Turn bag right side out and admire its generous dimensions.
Get the attention of your favorite football fan (rear-end of dog optional)
Delight him with his new lunch bag. Recall high school genetics and appreciate why your daughter is a bit stoic.