ER, Golgi body and other membrane bound organelles often work together to produce a finished functional product. What structure connects them?

The ER synthesizes most substances of the cell, and then the Golgi body ins the one to classify, distribute, and modify them.

The proteins forming the cytoskeleton are the ones that hold everything in place.

The main proteins doing this are the microtubules, microfilaments, and Intermediate filaments.

Also, mention the carrier proteins, that move substances inside the cell.