Therm-a-snap bag. It's an insulated bag that folds flat. Made in Germany.

I bought one of these for the car years ago, but now I use it for trips to the grocery store. Using one of these means I don't have to go right home anymore. They work very well. I used it yesterday and after an hour the frozen food was still rock solid when I got home. Beats the heck out of using a cooler.

I could write a review, but this guy already has in his blog.
http://www.bookofjoe.com/2006/05/thermasnap_hot_.html

I use a couple of those in the summer. They are great.

Of course, my night trips to the grocery store have been between 30° & 40°F lately, so I haven't needed them.

"Of course, my night trips to the grocery store have been between 30° & 40°F lately, so I haven't needed them."

Tut. The 20 x 20" bag will accommodate a pizza box nicely. There is another thread going about how to get a pizza home.