My dad has always been the 'help someone when you can' type - having been a mechanic for years, he was endlessly fixing other peoples' cars and changing flat tires. He always told people just to pay it forward when they could. About fifteen years ago, he hurt his back, and now has a multi-level spinal fusion - no more changing flats and such for him.
The year after his surgery, I was on my way to work after a nail appointment with a friend from work. We had the same boss, who had a big crush on my friend. She was one tardy away from being fired - nothing my supervisor could do, since we were in a call center and time was tracked to the second. We were a few blocks from work, in a busy industrial part of town, and I got a flat tire just as the road narrowed from three lanes to two. I was at the end of that lane that was ending, being passed by cars going 50 miles an hour or more, as well as large trucks full of crushed rock and gasoline tankers. She called our supervisor, and he came out and picked HER up - and left me to my own devices, as I wasn't due at work for another half hour.
I couldn't call my dad, and was nervous about getting out there and changing the tire, which was on the driver's side and would have left me exposed to the traffic. As I am standing next to the car on the should, contemplating what to do, an old beat-up pickup truck, with fishing poles in the back, stops in the road behind my car. An older gentleman, and his six or seven year old grandson, get out, and with his help we get my tire changed safely. The spare, though, was also flat! He offered to follow me to the nearest gas station, about a half mile up the road, and filled the tire for me. I offered him money for his trouble, or at least to pay for the air machine, but he refused, and after a quick thank you for them both they got back in their truck and went off, I hope to catch some giant fish. They were my angels!
I've changed flat tires for several friends since then, and had to change my own once or twice. Never have forgot that sweet man and his grandson, though. Dad said it was his karma coming back around to him - he couldn't have done the job himself, but someone else showed up to do it for him. :-)