This strap is intended for Norah Gaughan's Brea Bag, but of course can be used for any. It is a bit stretchy, depending on your gauge. Here's how I did it:
CO 8 sts.
Stockinette stitch for 5 rows, beginning and ending with a WS row.
Now slip this little square through a d-ring. Pick up 8 stitches along the CO row, and now hold the two needles with 8 stitches each parallel. Row 6: K2TOG, one stitch from the front needle and one from the back. This is similar to a three-needle bind-off except that you are not actually binding off; you are keeping the stitches.
Row 7: Purl
Row 8: K1, M1, K2, M1, K2, M1, K2, M1, K1 (12 sts)
Row 9: Purl the first 8 sts, then place on holder.
Now begin making three I-cords, 4 sts wide each, starting with these last 4 stitches. This is what mine looked like mid-second I-cord: Make each as long as you like. Remember that it stretches. Do not break the yarn on the last I-cord. You will need it to finish the strap.
After all the I-cords are finished, braid them together, making sure that the unbroken yarn is on the far left.
Row 1: Purl across all 12 sts, which realigns the I-cords.
Row 2: K1, K2TOG, K1, K2TOG, K2TOG, K1, K2TOG, K1 (8 sts)
Rows 3-7: Stockinette stitch
Do a three-needle bind-off around the other d-ring, having picked up 8 purl bumps from row 3.