What is the most used term in American English from the items below:
I.e., someone who travels with the driver of a large goods vehicle and helps with the loading/unloading and other aspects of making deliveries.
Admittedly, I have never been to Britain, but I get the feeling that what you're talking about must be much more common there than it is here. As far as I know, most American drivers have to do the lifting themselves. Sometimes for large jobs they have additional people with them, who I might just call "helpers," but most delivery drivers I can think of are pretty much on their own.