I can totally relate to your situation Mr. D. Even at times, although you have a car, you have to go along with others' schedules. The courage to say NO is really, really difficult. But if you start at some point, people will find alternatives.

However, at the same time, when i didn't have a car, I also used to bother my roommates and classmates to take me to grocery, pick up this and that. I know I can never repay them, so, to give it back, i usually don't say NO. But at some point,  I have also developed that courage to say "NO" when the request doesn't align with my schedule.