Restaurants don't drive off to somewhere else the instant you step out of them.
This was directed at the OP who said taxi's are OK because you can call the taxi company, but self driving cars aren't because if you don't call before someone else rides in the car you're stuff will be gone.
My response is that a restaurant works the same way. If you don't return or call before someone else sits there, you're stuff will be gone.
Addressing your point, taxis and buses immediately drive off after you step out of them. Do you avoid them because of this?
I'm pretty sure this problem isn't nearly as big as you think it is.