I have twice parked in handicapped parking spaces while using someone else's car with a handicapped placard - both times it was my mother's car. Once when I was driving her to the store and dropped her off at the door, but I knew that she would have to walk back out to the car. Another time, it was raining pretty steadily and I was driving her car to drop some stuff off at the recycling center for her. I was hoping to beat the rain, but I did not, so I went to a Walmart to 'wait it out'. I was visiting her from out of town and had no rain coat with me. I also had thrown my back out pretty severely a few days earlier. Sitting or driving a car did not bother it in the least, but walking and going from standing to sitting and vice versa was excruciating. I was able to use a shopping cart once I got into the store, but getting from the car to there was an adventure! So I did use a handicapped space for myself solo in that one instance.
Most of the time, I usually pick a space pretty far away form the store and walk all of it when my back is healthy.
This reminds me of another story though. One time before I had done something similar to my back and had to resort to using a cane to get around for a week or two. Even with the cane, I had a very noticeable limp. I was out for lunch with my family and a young man noticed my limp and my cane and he approached me, and asked me if I was injured in the service. Based on his demeanor and lead in - he was obviously prepared to thank me for my sacrifice. I admitted to him that it was nothing like that and just a back injury, but I acknowledged to him that there are many who have physically sacrificed quite a bit for our freedoms and although his assumption was wrong in my case, his gratitude toward someone he thought had made that sort of sacrifice was very well placed.
So let me pass along his gratitude to any others injured while serving our country.