I itemize major components (mixers, amps, snakes, etc.) but not the little stuff. It goes into a category called "Installation hardware." I don't use a percentage of the equipment, but have gotten really good over the years at estimating about how much I'll have in patch cables, wire ties, etc. Then I add another $100.00 to be safe.
Itemized vs. non-itemized? Just depends on your practices. My pricing on equipment is MAP so I don't worry too much about the customer price shopping me on the internet. My nearest and largest competitor doesn't itemize and I've been told by many a customer that they don't like the lump sum approach.
I can see pro's and cons to both methods.
As for selling the cheap stuff? Not going to happen with me. Any time I have sold cheap gear I've lived to regret it. And when it doesn't perform up to standards the customer never says "I guess I should have spent more on the gear." What they do say is "That guy sold me a piece of crap. I'm never going there again."