When I have a large amount of garden waste to take to a recycling facility, I pile it all up into a tarpaulin sheet on the ground near the car. Once adequately full but still manageable, I tie up the sides with rope and push/pull it into the boot of my car (with help of course!).
Once at the recycling centre, pull the closed tarpaulin out of the boot, drag it to where you dispose of the waste, open and ditch it's contents in one go. I find it far easier and cheaper than refuse sacks. Just an alternative suggestion which may work for you.