Essential Tools and Parts
I use the following products exclusively on my own car, and you can too. (The Amazon links are NOT affiliate links, and I get no kickback from them. Buy the products locally if you can.)
For general parts cleaning and a thousand other things, I use GumOut Carb and Choke Cleaner. For lubricating most parts that slide, or any small part that rotates, I use Super Lube. It's safe for plastic, good in freezing temperatures, and clear, so your clothes don't look like a superfund site. Every first-time Air-Schooled student must have those two items, and a roll of paper towels.
For harder-working metal parts like wheel bearings and CV joints, Valvoline Durablend Semi-Synthetic grease works great. For a few bucks more, I prefer the slightly more pungent smell of the Valvoline Synpower Synthetic grease, though I can not actually tell any differences in performance under 75mph/120kph.
One of my favorite tools, the best voltmeter I've ever used is back for sale on Amazon after a brief hiatus. It's a "pen type" meter, meaning you can always see the screen and the cords won't melt on the muffler while you troubleshoot a broken electronic ignition module.
I strongly encourage owners of fuel-injected Volkswagens to have a Bosch 2 Noid light for their car. This will save hours of time and frustration when diagnosing issues.