R&M Carrie, compact #cargoBikes with folding/locking box, only 18in wide when shut, handlebar stem folds so you won't get snagged on it in a hallway, roughly the length of a typical bike but you've got room for a child passenger and/or dog. Suspension fork, 80lb empty, $10k.

Folding (brompton) bike and folding (travoy) trailer. A nice ride to the store on a rainy day.

A DIY bamboo version of the handcart/bike trailer (using Burley travoy seatpost hitch.) Carbon fiber with expoxy resin, but I've seen this done with jute twine too and not so much effort on making flush joints.

(ab)using a cheap tubing bender for aluminum round bar. (I didn't know you could cold bend aluminum without cracking, maybe that depends on the type (alloy?) of aluminum.)

Cargo bikes don't have to be very wide. This build also reminds me of the argo kit, which allows your regular bike to convert to and from cargo mode.

The longtail Tern GSD #cargoBikes have a fold-down handlebar stem and are able to stand vertically on the tail. They're also short enough to get in some elevators without standing on end. ~$5k
(The handlebar stem is not awkward and fiddly like that if you flip the front wheel around to the other side when you have it standing up.)

Of course the HSD is even smaller than most bikes and still has enough cargo capacity to replace many car trips.

@enobacon I can vouch for the Tern GSD as a space-efficient cargo bike. I'm able to fit it in my building's tiny elevator, and it takes up a small part of my apartment front hallway. I don't use the vertical parking as much as I thought I would, but it's a terrific option. Particularly handy for cleaning and servicing the underside.
Also, all the cargo rack accessories are made with vertical parking in mind, so they actually offer better stability! πβ¨
@enobacon
After pulling a Burley Nomad for many years, I got a Burley Hopper, and I heartily recommend it. I use it as a shopping cart when I get to the store. Load it up at the checkout, then bike home and roll it up the elevator in cart form into our condo.
And it does fold pretty flat, too!