The Clyde Puffers had a crew of 3 and capacity of about 6 TEU
Wage bills have been a factor driving for ever-larger lorries and container ships. The transport companies have successfully externalised the knock-on costs of ever-larger ports, depots, and warehouses, and the impact on city streets. Removing the wages bill could open the way to a radical reduction in size. The perennial problems of inter-modality could perhaps also be eased. Changing the scale of logistics could open the way to better 'last mile' operations.
Using cargo bikes to replace or complement vans is an example of the scope for changing scale, and thought is being given e.g. here for the need to standardise small containers (no I'm not proposing autonomous cargo bikes for city centres). Such containers will hopefully be compatible with urban mobility platforms on the lines of M.U.L.E (not the US military MULE project).
Thanks to @thinkdefence there is a discussion of small container standards; see the section on JMIC. These would be great for mobility platforms but are not for cargo bikes.
The huge electric autonomous trucks being investigated in the USA may have a long-haul role there, but perhaps the real market is for something much smaller.
If delivery drones are ever to gain scale, there needs to be standardised landing pads, preferably palletised and compatible with small scale standard containers e.g. biscuit tins.
More speculatively, we can envisage a 21st Century replacement for the Clyde Puffer; small Autonomous Ro-Ro vessels (Damen have some starting points), some Mexeflote where local infrastructure is missing, and M.U.L.E like platforms to local depots.
Operations at this more human scale are likely to be more sustainable, and with lower knock-on costs. The trick will be getting the incentives right for it to happen, supported by timely standardisation.