I travel to most jobs in a Chevy Suburban with the seats laid flat. With all the equipment loaded, I have very little room left. I have been needing a rolling cart for a long time, but the ones that fold small enough are either way too flimsy or way too expensive (as in $1,000). Usually, I end up borrowing one from the shooting location when they have one. The last one I used was very small and two of the wheels kept falling off at the slightest bump throughout the three days of shooting.
Today, I saw a great solution at Costco called the Origami Rack. The Costco version already has rolling casters (although you will probably want to consider putting larger wheels on if you will be on any terrain rougher than interior floors or concrete sidewalks). While it is not as heavy duty as the $1,000 version, it is an amazing cart for the price of just $50. It folds flat for transporting and is super simple to use. The one I am referring to is the medium sized cart in the photo above. Check out the video here.