This really seems like an intriguing hobby. I'm honestly somewhat shocked this is a service that Amtrak offers at all.
https://www.amtrak.com/express-shipping
There's a 500-lb limit on each shipment, between more than 100 cities. An option for those not in a hurry, or who want to avoid driving the stuff.
The main restrictive thing, to me, is the list of prohibited items. Everything from stamps to watches to poles, perishables, office equipment (calculators, computers, printers, telephones...), medicine, liquids, furniture, mattresses, appliances, electronic equipment of any kind (explicitly mentioning TVs, radios, stereos...) engines, motorized vehicles, fragile articles... the list goes on.
I literally can't think of anything that would fit those requirements that would be large or heavy enough to need to be moved by Amtrak.
[1] My friend rented the private car at cost from a friend of his for a family trip from Miami to Chicago and back. It was not cheap, but it was a rolling hotel (porter and chef, four bedrooms (one for crew), bathrooms, lounge, dining room and kitchen).
>Manila's 'trolley boys'
> One way to travel in the Philippine capital, Manila, is by trolley. Passengers choose this unofficial transport service because it's quicker and cheaper than other options. For the homeless community that runs the illegal service, it puts food on the table. But it's also incredibly dangerous.