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.