Shortly after I got my E, I went to Walmart, with hopes of buying some sort of net to hold groceries from doing the thing you mentioned.
I found they sell a device that has three compartments made of netting with a platic tubular frame that works great. I found it in the automotive section. It came with velcro strips so it can be anchored to the floor and doesn't slide around.
When I unload the groceries from the cart, you just open the top portion of the clam shell in the rear and set the bags in the three compartments and "away we go"... Works great and was only about $14.00.
I also added an industrial type floor mat for under the back see that provides a non slip covering. It was about 3'X5' in size. Works great and was about $17.00 from Costco.
I bought a gray utility carpet (27"X47" I think) at Linens'nThings for $9.99....works so well I went back and bought another one for when I have the seats out or hung up to protect the floor from scratches and prevent the cargo from sliding.
I did also order the Honda Cargo organizer from H and A.....this works well for groceries and other shopping (ie Target or Wallmart).....plus it works great for keeping my car washing supplies and a few other items....
We don't have a garage, we live in a town house...so it works well for us.
Plus the cargo organizer just un snaps for easy removal and folds up for easy storage.
Also I believe the rugs that I bought at Linens'nThings were caller Duramats. They are almost the exact color of the floor.....but also come in taupe and huntergreen.
I bought "shelf paper", it is actually a rubberized material that is used on shelves and in tool kits. Lowes has it in the shelf department and it comes in many different colors. I bought black/charcoal to blend with the interior of my E. Also used the same material in the dashboard trays.
I purchased a bunch of carabiners at Home Depot (99 cents each) and clipped them to the seat bungee on the back seat. I clip them to the grocery/shopping bags to keep them from sliding around. It works great. Using this method when I have to put up the seats for my bike, etc...... I don't have to remove any containers.