This is probably one of my favorite things about owning a car, and why I have a sedan vs. a hatchback. Being able to store emergency supplies (couple cases of water, a backpack, ...), personal tech supplies (spare mbp charger, cable toolkit, etc.) in my car makes life much easier. Realistically this is 100-200 pounds of stuff, and I wouldn't want to have to carry it to/from a car myself every time I got a robot car.

The use case I'm imagining is people going shopping, and wanting to put bags from one store away in their car before going into another. So what if you could summon up a self-driving car, put your stuff in its trunk for a fee, and then call back the same car later with your stuff still in its trunk? It could go be a taxi while you're busy shopping, and not allow other customers to unlock its trunk.

Or we'll get a car design with a removable trunk.

I think you're spot on.

But I think the removable trunk will be combined with a passenger-less unit that carries the trunk back to your house and drops it off. Sort of a tiny version of container shipping.

That sounds like something that might happen in the farther future, but I expect there will be a lot of general-purpose auto-driving cars made before companies start making super-specialized models like that.