Probably the biggest bang for the buck regarding the electrical system monitoring would have to be adding the EI volt/amp meter.
It's an easy install, not that much in terms of cash outlay and it's digital for both volts and amps which does away with the guess work associated with a needle and the angle your eyes look upon said needle.....it has a warning light as well to draw your attention to it if your scan isn't up to snuff.
It's the instrument in the top right corner in the picture.
