I recently unearthed my Tunisian crochet purse  (from a planetjune.com pattern) and put the finishing touches on it.  The first thing I wanted to do is fix the curl on the front opening of the bag.

In the months since I blocked it, the bag has been carried around, stuffed into my project bag, and I sort of ruined the blocking by not keeping it flat.  Instead of re-blocking it, I decided to reinforce the top edge.

I added four rows of single crochet to the top edge.  Here is is as seen from the outside on the left and from the inside on the right.

Then I cut a piece of plastic boning (mine is Dritz Rigilene) to the length of the top edge.  You can see here that it's a flat and wide.  It's mesh-like plastic that is fairly rigid.

It comes on a roll, so there is a slight arc to it.  I tucked the boning into the pocket so the arc bowed out and sewed the flap down to cover it.

Ta da!  Now my bag has a nice flat edge at the front opening.