Lynne emailed and asked about how I made my denim grocery bags.  While I was answering her I realized I forgot to include something important in my post.

No matter what your brain tells you, it's impossible to sew denim straps inside-out and then turn them right-side-out like you do with normal fabric.  My brain kept telling me that the straps were totally wide enough to turn, so I didn't sew one and try it out first.  I sewed all four before I realized my brain was a big dummy.

Luckily, I use Blogline's super-handy "clip" function*, and I remembered that I'd just clipped a double-sided strap tutorial posted by Fat Orange Cat.  The tutorial isn't exactly what I did, but it gave me the idea of how to sew the straps once I seam-ripped all 12 feet of them.
Basically, I cut the strap fabric so it was two-times the width of the strap I wanted plus one inch.  (1) Then I folded in half an inch on each edge and ironed it.  (2) Then I folded the strap in half so the two half-inch folds were together on the inside of the strap.  (3) Then I sewed up each side.  Ta da.

*When you clip something in bloglines, it gets saved to your "Clippings" tab.  I've made a bunch of folders to save my clips ... "Stuff To Buy"  "How To"  "Things To Make"  Things I've clipped have come in handy several times!