Ultralarge ships (top 161 in the world edit: that number of ships is a decade old, sorry) all carry at least 5,000 40' containers (and up to 10,000). That sounds like a lot, but right now the Chinese factories are cranking out about the 600,000 a quarter. (Note, I'm talking about 40' containers, but the industry talks about 20' so you may find double my numbers on a search.)

They seem to cost about 2,500-4,000 to purchase new, so theoretically they could make 20-28MM loading them with empties (if they were worth the same as new). I don't know how long it would take to load the ships with cargo, but there are currently $24MMM (that's 24 billion) in goods anchored outside the port of LA waiting to be unloaded. So 3 orders of magnitude higher. How much of a premium must load/unload capacity be at right now?

If we weren't truck limited, we could just move all the empties far away and stockpile them until they can be profitably returned. But I know people who have tens-of-thousands of dollars in tons of raw materials (think universal inputs) stacked in a warehouse they have to vacate soon and they cannot even give it away because of transportation costs. They're going to have to pay someone to take away the things they (correctly assumed) they could buy for almost nothing last year and would be worth more today.