I can empathize as well--my first screamed in the carseat ALL THE TIME. She did get a little better as she got older, but really, it wasn't until we turned her facing forward that she finally stopped fussing in the car for the most part. We lived in a walking friendly community and I walked to as much stuff as I could so I could avoid driving.
Now, with #3, he doesn't like the car seat, and doesn't really fall asleep in the car (at least not in 10-20 min which is the most he's usually in there at this point), but he doesn't get himself as worked up as DD did and sometimes will make it for 10 minutes or so. But once we get where we're going, within a minute or two, he is fussing to get out. I've learned to always bring some type of carrier for him and just plan on having to carry him in the stores. Its a pain because it means I have to get him in and out of the seat, even if its just for a 15 minute errand, but he doesn't cry while I'm shopping anymore, and I have my hands free. Not sure if that would help.