I needed a bag that would hold a lot of stuff and be completely hands-free to wear, so this is what I came up with. I made the cream bag the night before a festival. My friend wanted a variation of the bag so she and her boyfriend could carry their snake around, so I made the green bag and documented it for all of you. :)

This bag seriously holds a ton of stuff.

If anything isn't clear, please ask. :)

Step 1: Materials and Supplies

You will need fabric for the shell (the outside of the bag) and the lining, and the strap. Actual yardage will vary depending on your size. Either the lining or the shell material (or both if you like) should be a heavier fabric, to support all your stuff. Both of the bags I made are lined in a heavy duck cloth. The cream fabric is muslin, which makes the bag softer and slouchier, and the green fabric is a bottomweight, which makes the bag stiffer and hold its shape more. Whichever fabrics you choose, they should not be knits or other stretchy fabrics.

- For the template, you will need a piece of cardstock or construction paper about the size of your back. Tape two pieces together if you need to.
- For the body of the bag, you will need about half a yard each of the shell and lining materials, from 45" cloth.
- For the strap: Measure from your right hip, over your left shoulder, and back down to your right hip, and add 12 inches. This is the length of strap material you will need. The width is 6 inches. Yes, you have to buy a lot of fabric and will have a lot left over, but Jo-Ann's has coupons every week so it won't be too expensive.
- Notions: thread to match lining and shell; depending on which closure style you choose you will need two D rings or two buttons and some elastic cord.
- The usual miscellaneous things: pen, scissors, pins, etc.

Step 2: Make a Template

First, make a template for the body of the bag; you'll need a friend for this. Either have a friend hold the cardstock up to your back and trace the shape, or you do the same to your friend (it helps if the friend is about the same size as you). You are making a rectangle with smooth rounded corners. Don't worry about symmetry right now; we've got a trick for that in the next step.

Mark a 1/2" seam allowance around your template, then cut it out. (I didn't do this and had to add seam allowances to my fabric before cutting, and it was a pain in the neck.)

Roughly sketch a diagonal line across your template to represent the top edge of the front piece. Sketch another line 1/2" above that for your seam allowance.

Step 3: Cut the Fabric Pieces

Use the template to cut two pieces each from the lining and shell. To make your pieces bilaterally symmetrical, fold the template in half and place the crease on the fold of the fabric. Remember, you can fold the fabric wherever you like to make it most economical. Trace and cut. Ideally you'd use a pencil or chalk, but if you need to you can use a pen since the marks will be in the seam allowance. Disregard the added seam allowance marks in the pictures; I was foolish and didn't include them in my template.

Out of the pieces you've cut, one each of the shell and lining pieces will be the "back" pieces (whole rectangles, touching your back), and one each will be the "front" pieces (trianglish shapes, not touching your back). Using your template as a guide, cut one each of the shell and lining pieces along the diagonal that is marked on the template. You can use the first as a template for the second to get a perfect match. If your fabric has a right and wrong side, you will need to pay attention to which way the diagonals on the front pieces run. With your fabric right side up, lay the template wrong side up for the lining and right side up for the shell.

Finally, to make your bag hold a lot of stuff, you will need a rectangle of fabric to give your bag depth. Measure around a front piece from corner to corner the long way (not across the diagonal); see the last picture for clarification. Add an inch for wiggle room, and that is the length of the rectangle. The width is four inches (three inches of depth plus seam allowance), though you can make it wider or narrower if you like. Cut one each of these rectangles from shell and lining material.

Step 4: Pin and Sew the Shell and Lining Pieces

The right side of fabric is the pretty side, the side you will see. The wrong side is the ugly side, which will be trapped with the seam allowances between the shell and lining and won't be seen. This part is tricky, so read carefully. For the shell, you will pin right sides together, and the shell will get turned inside-out. However, for the lining, you will pin right sides together, but it will not get turned inside-out, because the interior of the bag is the pretty side. This means for the shell, the right side is the OUTSIDE of the bag, but for the lining, the right side is the INSIDE of the bag. The pictures and notes will help you a lot on this step.

Pin the front, rectangle, and back lining pieces right sides together, as shown. Mark with ruler and trim excess from rectangle piece. Sew with a 1/2" seam allowance.

Repeat with shell pieces, noting that the diagonal should run the opposite way.

Step 5: Attach the Lining to the Shell

Clip the curves of both pieces.

Insert the lining into the shell, right sides together. You should see the seam allowances on the outside and on the inside of the bag. Pin all around the edges, but leave a gap about 4 or 5 inches wide at the bottom of the diagonal (see pictures). This is the opening through which you will turn the bag right-side out.

Stitch where pinned, with 1/2" seam allowance. Clip the curves.

Reach into the gap and turn the bag right-side out.

Fold the raw edges of the gap inward and pin to match the rest of the edge. Topstitch close to the edge.

Step 6: Cut, Sew, Attach the Strap

Cut two strips 3" wide, and the length that you determined in step one. Sew them right sides together, 1/2" from edge on three sides, leaving one short end open. Clip corners on the closed end.

Turn the strap right side out through the open end, as if inverting a tube sock. This is very tedious; I'm sorry. Tuck the raw edges in and topstitch to finish.

Lay the strap on the back of the bag and pin in place. Try it on and adjust as needed. For the cream bag, I had 16"-13"-30" (below the bag, across the bag, above the bag), and for the green bag I had 22"-12"-35".

When you've got the strap pinned where you like, stitch a rectangle to secure it to the bag, making sure to pull the front of the bag out of the way so you don't stitch it shut. If you want to be fancy, put your strap thread on top and your lining thread on the bobbin, and it will look super slick. I wish I'd thought of that before I finished. If you do this, be sure to test your tension on a scrap so you don't end up with loops of one thread showing up on the other side.

Step 7: Finish the Body

At this point all your stuff will fall out of the side of your bag, so you must close up the side. Pin the back to the rectangle and the front as high up as you'd like. The higher you go the more secure, but the more narrow the opening. Of course we will also install a closure in the next steps.

Topstitch closed. Stitch the same distance from the edge as you did when closing the gap earlier, so your stitching will go right on top of that stitching. You could whip stitch or slip stitch by hand if you prefer, but I don't think it's as secure.

(In these pictures the strap isn't attached yet; I then found out you have to have the side open to stitch the strap on, so I had to rip out my stitching and redo it after adding the strap. And that's why you shouldn't start a project the night before an event.)

Step 8: Closure Style 1 - D Rings

This style of closure has a strap and two 1" D rings.

Cut a 2x4" strip to secure your D rings. Fold 1/2" inwards from each edge and press. Trim the corners. Then loop through both D rings and line up the ends so you are left with a strip 1.5" long. Pin, then stitch around in a square to secure. Take care that your D rings are clear of the presser foot; it helps if you start your stitching on the side next to the D rings. Stitch the D ring tab to the top "lid" of your bag.

Cut a 2x13" strip for your strap. Fold 1/2" inwards from each edge and press, and trim the corners. Then fold in half to get a 1x6" strip, and stitch all edges. Stitch the tab to the lower edge of the bag opening, across from the D rings.

To close, thread the strap up through both D rings, then down through only the lower D ring. Pull tight.

Step 9: Closure Style 2 - Loop and Toggle

For this style of closure, you will need two buttons and some thin elastic cord.

Tie a loop with the elastic and secure the knot with glue.

Place one button on top of the knot of the elastic on the top "lid" of the bag, with the loop pointing toward the edge. This button isn't necessary, but it covers the knot and looks pretty. Stitch the button to the bag, stitching to either side and in between the loop ends (just below the knot). This should secure the elastic as well as the button.

Stitch the other button on the other side of the bag opening.