Here comes the pictures. They are simple nodes that can be hidden and shown.
Roadworks:

A big barrel for liquids:

Drums for fuel, tar, or explosives:

Crates for stuff (I need some ideas what to put in them, I was thinking about vegetables or fruits, but I need textures!):

Last but not least, boxes for generic delivery needs:

Known issues:
If you repaint the truck with the box or the barrel on the loads change their colours too.
Feel free to suggest more kinds of cargo.