Instead of trying to pack dirt, christmas trees, junk or over-sized items in your car, use my truck with 8 ft bed.
Truck has tie downs inside bed and ratcheting straps are supplied. I have some moving items I can loan you such as flat 4 wheel dolly, handtruck, moving blanket if you ask for them and return them.
There is room behind the cab to put some stuff like luggage, tools, etc. I am 6 feet tall and weight 200lbs and can lay down behind the seat. No, I wouldn't want to go too far like that but it can be done. :)