Simple Solution for Unforeseen Groceries

I have now stopped using the Urbana bike that I was test-riding in April and have gone back to my Gazelle. While overall I prefer the Gazelle, I do miss some of the Urbana's neat features and have been trying to devise ways of making the Gazelle just as accommodating. Among other things, I want to find a DIY solution that will emulate the utility of Urbana's fantastic rack that accommodates any grocery bag without requiring panniers. I thought hard, but could not come up with anything... until fate did it for me. If you haven't fainted yet from my use of plastic bags, perhaps you'll appreciate this.

Yes, two bags tied together and turned into "panniers." It was totally impromptu. We were cycling past a grocery store just as it was about to close, when we realised that we had neither anything to eat at home, nor anything to carry it in if purchased. We ran in and bought some food, thinking we'd carry it home on the handlebars. But then, in a flash of brilliance, the Co-Habitant created the objet d'art you see here. We cycled home ridiculously happy. I guess this is what one of my readers meant when he wrote that "a peasant in any number of countries with a million plastic bags can figure out and equal number of ways of carrying their stuff."

Question: Why would one even buy dedicated grocery panniers, if they can take a pair of reusable canvas bags, connect them by the handles (with an S-hook or a bungee cord), and secure them to the rack either via rat trap or via the same bungee? I realise that the plastic bags in my pictures look horrible, but a pair of nice reusable shoppers could look as good as panniers while also being more versatile and costing just a fraction of the price. Does it just not occur to people in the same way it did not occur to us? While I am delighted to have this method of carrying groceries in a pinch, I am also feeling foolish that I did not think to do it earlier. It takes skill to recognise simple solutions, and that's a skill I would like to develop.