Yes we all give away some parts, HDMI cables, etc. Before I start any work the client has a 'ballpark' of what it will cost them. When I give that cost I cover myself on the incidentals because, after all it's part of what I will use in the work process. When all is said and done and I am getting paid I can usually tell the client "by the way I used an extra 2 HDMI cables and walllpates, but no charge those are on me". Who doesn't like getting their money's worth and getting a couple of tidbits for free.....leaves a good impression and creates referrals.
Of course, ymmv.