Phil Wood grease, purchased from Ann Arbor Cyclery in about 1978.
I couldn't have imagined then that this mundane purchase, one of a thousand or so similarly forgettable items I must've also bought that year, would follow me around for 35 years and that in 2013 I'd still be using it to lube pedal threads. (A bit less remarkably, I still have the Campagnolo Nuovo Record low-flange front hub that I got that same day, but it hasn't been ridden in years. Lots more use out of the grease.)
I don't rebuild many hubs or headsets nowadays, so I don't pull this out of the tool bag very often and there's a good chance it will last me the rest of my life.