I always ask if people need help although usually I hope they don't since it will effect my ride. I hope that other people will ask me although there's not much anyone can do for me on the road that I can't do myself. I frequently get people in cars offering me a ride or a cell phone.
Other than on group rides, I've only been taken up on my offer twice. Once was a new rider who had a flat and no tools, spare or patch kit (which was fine since she didn't know how to use them anyway). I showed her how to change a tire and got her going. She was going to ride right to the shop where she bought the bike to get what she needed and to have them show her how to use everyhting. I would have thought they'd have done that when she bought the bike before she left the shop for the first time.
In the other case it was a guy who was walking pushing his bike. I was in my car, but had my bike tools in the back. Unfortunately his tire was wrecked beyond repair. I gave him a ride to his house.