Today I was riding and I saw a car pulled over on the shoulder with a flat tire. Luckily the car had a jack and tire iron in the trunk, and I knew how to change a flat tire. The driver didn't know how to change a flat tire, and she was grateful that I had stopped and changed her tire. I didn't expect anything in return. I turned down her offer of a ride to my destination 15 miles up the road, because I wanted to ride my bike there.
Most car drivers would not stop for a car stranded on the side of the road, but a bike rider can't miss an "obstacle" in the shoulder, and it's easier for a bike to stop and help. When I'm on my bike, I tend to stop every time I see a car pulled over on the side of the road and ask if they're ok.