I got a couple of large cheap sports holdalls from Sports Direct for carrying my par cans around in. They were much, MUCH cheaper than anything that you'd find if you searched for "PAR CAN case". The original, individual cardboard boxes provide a bit of padding for the lights, and in turn are protected by the holdall. Having only two lights in each holdall makes them easier to carry around & stack in the car, as individually they are not too big.
For mic/leads/gaffa tape/spare strings/etc. I recently bought a small flight case like [url="http://www.pulse-audio.co.uk/5051259010635.shtml"]this[/url], which is actually quite robust.