North America has lots of land and oil. Timber (Canada), plastics, and corn fertilised by nitrates that were made using fossil fuel energy. Corn probably doesn’t ship in containers but corn-fed beef and poultry do?
Some import products are crazy cheap because cross-planet shipping is basically free because it's the reverse end of a trip carrying valuable stuff. But they mainly applies to ships returning from low development level regions.
While the majority is bulk, the US does export a lot of industrial machinery. It's just not stuff you normally think about - like the large hvac systems on the roof of large buildings or the caterpillar earth moving equipment/parts to make roads.
