I've imagined a sub-car-sized delivery drone. Think one or two-wheeled drone that arrived outside with your bread and milk. Impacts traffic less, you don't need to be driven, makes smaller purchases more economical.

You could have a postbox-like port that it could put items into.

You mean like self-driving motorcycle? Why won't people just get on a bike, and pick up small items themselves (+health benefits, sustainability)?

Convenience, safety and lower costs. When you're cooking and you forgot some ingredients, push a few buttons and 10 minutes later your order arrives, sans humans and hassle. Like pizza delivery, but for everything and with fewer costs. Lower costs mean smaller transactions become economical. No flying bladed helicopters mean reduced risks and requirements for landing spots.

We have grocery delivery in my area, but it's such a hassle because I have to be home within their time window and I have to book it a couple days in advance. Why can't I just hit a "now" button and it arrives via drone, at 2am if I so desire, when most delivery people are sleeping? Or in a rainstorm, because the drone doesn't care?

Maybe the people have reduced mobility. Maybe they have small kids or elderly people they can't bring with them nor leave alone. Maybe they have an extremely busy schedule. Maybe the streets where they live are dangerous for cyclists. Maybe the packages are too big to safely carry on a normal bike. Maybe they just don't have a bike or even know how to ride one. Maybe they just don't feel like it.

It could work better with residential buildings, I think.

Our building doesn't have a helicopter landing pad or anything that fancy, but it's fairly clear and well-maintained (no debris or trees growing up there). There's no reason a relatively light drone can't land without issues.

Exactly. And if it's big enough, it becomes really hard to steal and it can transport some sort of locker that the client can open.