I didn't have any cord to use to make my own piping or welting, so I had to get creative if I wanted to avoid another trip into town. So I decided to try making denim fringe piping, and it turned out well. Here's how I did it:

I cut one leg of an old pair of jeans into two-inch strips (crosswise cuts, perpendicular to the outside seam). Then I cut out both seams so I had two flat strips per original piece.

I folded each piece in half, and pressed it. Then I sewed through the middle of each strip, creating a folded side 1/2" wide and a side with two cut edges 1/2" wide. I had bunches of strips since I cut a whole leg for this project, and I just kept the thread attached between each piece, so they were strung together like sausages.

Then I clipped the cut edges, roughly every 1/4 inch. I ran the strips through the wash with other jeans (I purposefully washed them with heavy items to encourage fraying). Then I put them into the dryer to finish. The strips frayed up nicely, although not completely-- that will come with wear.

When they came out of the dryer, I had to iron them-- the cut edges had flipped outward, toward the fold. I had to iron them back flat so I'd be able to insert this fringe into seams without sewing over the frayed part.

Here's what it looks like on a work in progress:

Pretty cute, and it seems to work well to reinforce and protect the edges. And the more beat-up the item gets, the more the trim will fray, and the better it will look. It's also very convenient that you don't have to worry about stitching together continuous trim-- just butt two pieces together and sew, once can't tell from looking at the fringe where one strip ends and the other begins.