Great question for a new topic!
I use a variety of oils and greases for different purposes, but if I had to list a "favorite", I'd say it's Anti-Seize. The silver stuff that comes in a small tube.
I actually keep a very small brush right next to the tube in a tray in my toolbox, and there is always a bit of anti-seize on the tip of that brush.
On kart engines, I will alway brush a bit on spark-plug threads, case screw threads, and barrel and/or head stud threads before assembly. It's actually very rare that I don't coat fastener threads without a little touch of it. On the kart itself, the axle will get a very light coating where it rides in the bearings, and I will usually apply a very faint "haze" of it where brake and sprocket hubs clamp to the axle. I most definitely always apply it to the threads of the pinch-bolts on the rear hubs.
Essentially, pretty much anything that I want to be able to take back apart easily gets a faint coating of anti-seize. It's my most useful (and probably most used) lubricant.
PM