A beginning or intermediate sewer can make this bag in about two hours. The most difficult part is sewing over the several thicknesses of fabric. Some parts will need to be stitched by hand if they are too thick for the machine.
Step 1: Cut the bottom 8 inches (or however deep you want your bag to be) off a pair of army coveralls. Jeans would work as well, but wide-leg jeans are much better so the bag is easier to turn when sewing.
The size of your bag will be determined by the width of the pants. This bag will be about 7 inches wide. You can make it as deep as you like, but it's simpler to add decorative elements if the bag is somewhat shallow. This one is cut at about 7 1/2 inches, so the finished depth is about 7 inches. It is easy to cut evenly if you have a rotary cutter.
Step 2: You will not have to seam the sides of the bag; they are already done as part of the pants. The top edge of the bag is the hem of the pants, so that is done as well.
Turn the bag inside out and seam the bottom edge of the bag together (the part you had cut). I use a half-inch seam. Reinforce with zigzag stitch, since the bag is not lined. Turn back to right-side out. The bag will now look like the above photo.
Step 3: If you are adding decorative fabric, cut it to the size you want. I used old dresser pieces that had holes in them (99 cents at Salvation Army).
I didn't want to cut away the pretty curved part of the embroidered cloth, so I wrapped it to the back of the bag.
Step 4: Pin the decorative cloth to the bag. Baste by hand, unless you are confident the fabric will not slip during stitching.
Step 5: Sew the decorative fabric to the right side of the bag. As you sew, the bag will need to be turned inward so you can reach all parts of the fabric.
I sewed the edges by hand, since the thick parts of the seams were too much for my machine.
Step 6: To make the strap, cut three one-inch-wide strips of cloth from the leg of the pants. I like to make the strap as long as possible, so the bag can be cross-body. (This one is not that long). Make your braid flat and tight. It's easiest if someone holds the end for you. To sew the strap onto the bag: fan out the three parts of the braid so they will be easy to fit under the zipper foot. Sew onto the outside of the bag (for texture and because it's cuter that way). Back-stitch so the strap is very secure.
(My designs are sold at Les Junc, Zimmerman, MN, open every Saturday from 10 to 4).