Take a place mat that is not too thick and fold it in half so that the sides of the placemat are now the top of the bag. Sew a 1/4" seam on both sides. Now we have to make a small seam so that the purse will be flat on the bottom and can sit upright. To do this, bring the bottom corner on the right side and make it come to a point by pulling it to the right side. Draw a line on the point where it measures 3". Sew on that line making sure to backstitch at the end of each seam. Do the same thing on the left side. See picture #2. Now turn the bag right side out.
To make the straps, cut 2 pieces of fabric 4" x 16-18". Iron some medium weight fusible interfacing on each of the pieces of fabric. Iron the straps in half lenghtwise, then open them up and fold the raw edge in until it touches the center crease you just created by ironing it in half. See picture #3. This should make your straps approximately 1". Take the strap to the machine and topstitch along all the edges. I like to use a Bernina foot #10 - the edge stitch foot. It has a rudder and you just butt the edge of the fabric up next to the rudder and it makes it really easy to sew close to the edge and sew straight. Now take the straps and sew them on to your bag. Try to measure an equal distance from the center point on each side of the bag to find the placement for the straps. On the sample, I sewed the straps on the outside and then added buttons for decoration.
But you can sew them on the inside and not have to put a button on it. I measure the bottom of the bag and cut a piece of cardboard from an old 3 ring binder to fit the bottom and give it more body. The measurement is somewhere around 3" x 9". Cover the cardboard with fabric - picture #4.
These bags are very easy to make and can be embellished with flowers, buttons, embroidery or whatever you choose.