Probably my original chrome FM2n. Bought it used in 1991. Traded it and a black FM in on my first F3P in 2004. Only got $80 in trade value for it, so probably should've put it back into the bag, along with the ugly 55f2.8 Micro, which I eventually got back. At least, the black FM2n that I have today does a pretty decent job at satisfying my desire to use an FM2n. It's nowhere near as clean cosmetically, but works fine.
Lens-wise, probably the 35f2 Nikkor-O AI'd. Am trying to buy my last one back, if Glazer's can find where they have it. If not, when they get another 35f2, I'll get that one instead.
I've been pretty good lately, at avoiding the urge to purge, then replace. Most of my Nikons are purchases from 2007 or 2008. The only 2009 purchases have been the Nikomat FTn and the EL. One body is one that I've owned twice, namely my F4. Bought it in July 2007 for $200 as an F4s. Traded it and some other items toward my F2A and a 35f2 Nikkor-O (not the same one, but one that donated its AI ring to my last one). After Christmas 2008, I noticed that there was a familiar F4 at Kenmore Camera. Turned out that mine had returned, this time with a MB-20. Traded the F5 toward it, and never looked back.
-J