But how? If you can't walk more than X steps, and can't start the car because that's the equivalent to 'starting a fire', how do you get there? Is it OK to take a cab or bus, because then some gentile is 'starting a fire'?That is a good question and kind of what I was thinking too. There also was a part about not taking things from private to public domains unless it doesn't leave your person, at least that is how I read that, so to me that would mean you couldn't leave your towel/bag on the beach either. It is very interesting and seems very complicated to follow 100%, it would be hard to analyze all the small details to ensure compliance.
It's complicated, in part because the definitions of public and private domain aren't obvious. There are ways that people define large areas as within those domains--large areas meaning entire neighborhoods. (Google "eruv" for more information.)
I've had observant friends arrange to go out for dinner in a group (if people were going anyhow), and arranged for someone to pay their share of the bill and get the money back after sundown Saturday, so the observant person wasn't carrying money on the Sabbath.
From another angle: a disabled friend of my mother's has special permission from her rabbi to take a taxi to synagogue for Sabbath services, because she and the rabbi both think that going to services is more important than not riding in a car on the Sabbath. This is pre-arranged with the cab company (I think she has given them a credit card number) so carrying money isn't an issue.
Part of the complication is that along with broad patterns, there are endless variations in how people practice.