BTW, for the use on those little TA racks some French companies made even smaller bags. I stumbled onto a couple when in Saumur last year and bought them both.
They slip onto the rack's tombstone and are secured to the rack with a strap and a press stud. Room for a mini tool, a spare tube, a banana and even a lightweight rain jacket:
Just slip them on, close the fastener and off you go:
