Milk crates zip-tied together on their sides so that a bench seat fits on top and red bins from Lowe's can slide inside them. I don't have any milk crates, though. I also don't know what "zip-tied" means. I would use different colors.
DIY crate seats - these may be way better than the couple of rickety old chairs in my room I usually have students use at my desk. Using a picnic table cloth for easy cleaning coverage and adding casters to the bottom.