What TJC said - particles generally settle at the bottom of the pan and are suspended in the fluid reservoir. Draining removes a good portion of those. Flush stirs all of that back up and reintroduces contaminates into the workings.
12v Air compressor is the most used tool I have in any of my vehicles.
I'm still trying to figure out my tool load for the Ranger as well. Right now I have a small 1/2"socket set, air compressor and tow strap. Will add Screwdrivers, needlenose, channel locks, nut driver to fit any hose clamps.