So today I got them ready and loaded them in the back of my car and headed to the store. Then I promptly forgot to take them inside with me. I decided that I would just tell the clerk to put my stuff back in my cart with no bags (like at Aldi's or Sam's) and then bag them in my own bags when I got to the car. I've never gotten such a funny look in all my life--apparently I'm the first person who's ever asked her to do that. I explained that I'd left my *new* reusable bags in the car and asked her if there was any special procedure for bringing those in with me. I wondered if she would think I was a total freak at that question, but she seemed quite familiar with that scenerio and told me all about how easy that was. So we'll see if I can actually remember to take them in with me the next time around!
They are quite handy bags though and seem very sturdy (obviously stretchy!). Here they are with all my stuff: