I recently left a gallon of milk in my trunk and forgot about it until the smell started. I didn't realize what it was (I thought the kids had left a sippy cup somewhere) until I went to fill up my gas can and saw the exploded gallon milk jug.
I took everything out including the spare and sprinkled the carpet with powdered laundry detergent and hit it with the hose, I did the same with the carpet and spare tire lid in the driveway, then used the shop-vac to suck up the excess.
That got rid of most of it.
Try not to get the electronics on the back wall of the trunk wet.
