Boo, this is a great tip. I began keeping a very large rubbermaid type plastic storage container without the lid in my trunk years ago ... originally intended for grocery shopping to keep groceries from rolling around the trunk but it has come in handy for so many things. It's really great when I go nursery shopping, keeps the plants contained for the trip home. Cardboard boxes are great for some stuff but if you have plants with wet soil the box can get soggy so I prefer the heavy duty plastic containers.
I have to admit though .... there have been times when I've *um gone a bit overboard with plant purchases and also have to put plastic on the back seat.
