Lee Valley is offering this Trunk Organizer/Storage Bin for only $13.50 (USD).  My personal experience with Lee Valley has always been good.

Lee Valley Trunk Organizer/Storage Bin

From Lee Valley’s description:

This is a product anyone can use. We designed this soft-sided interpretation of the ubiquitous milk crate after finding similar products to be overpriced or poorly executed. This one has hinged rigid panels to give the sidewalls support, while allowing the two-compartment container to collapse into a compact 3″ thick bundle, making it easy to store (and easy for us to ship!).

Made from a tough woven polyester, it has padded handles and piped edges, and measures 23-1/2″x13″x7-1/2″ when open. The coated interior surface helps to contain any spills, and makes it easy to clean. It is ideal for use in a car or truck, holding all sorts of items to keep them from sliding or rolling around as you drive, particularly for keeping grocery bags upright. In the home, it?s as useful as a basket for both storage and transport of anything from woodshop offcuts to children?s toys.

via Trunk Organizer/Storage Bin – Lee Valley Tools.

Some caveats: There’s no lid, so it’s either got to end up on the top of things – or at least without anything on top of it.  On the  other hand – for quick hauling of anything – perhaps to and from a  vehicle, or other hastily assembled packages, one or more might do well kept in their folded state.  My calculations suggest about 2291 cubic inches; corrections or confirmations from readers welcome.

And here are some additional images: