I think trams and buses work well, too. Of course buses are getting closer to autonomous taxis, but it still feels more efficient to share a bus than to have one person per taxi :).

Then of course they can be used together. In my city there is a system of rental cars that you leave at different stops: you have a card and can just take the car if it's there. The car doesn't come to you, but still it's a pretty good solution I think.

Anyway, autonomous cars have to get reliable before they can actually be used with public transports, I guess.