Such decked-out rides are a little more streamlined for a city-goer who
doesn't want to take up half the road with a tricycle. But freight
attachments can be expensive since they're often custom-made. So many
San Francisco denizens opt for the generic version: A milk crate lashed
to the back of the bike via a bungee cord. It's a little less snazzy
but it gets the job done.
If you don't feel like hauling the weight yourself, you can still support cargo trike technology by hiring someone else to do the pedaling for you.