By oldest, I mean closest to beta/launch. My oldest item which I am still in possession of would have to be The Supremacy from the original Queen's Wrath event. I also have 2 Jackolytes and 3 Flight of Shadows.
EDIT: My other vanilla items are Deviant Gravity-A, Perun's Fire w/ Accelerated Coils, AOS#Cryptid gauntlets, Ghost Angel boots, Ghost Angel cloak, Dustwalker cloak and the vanilla titan IB class item.
EDIT 2: I forgot about my vanilla Dead Orbit and New Monarchy titan marks.
EDIT 3: Uploaded picture of my very first ever legendary gear drop : )
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Queens wrath helmet + robes. Lots of vanilla vendor weapons in my vault including an unfriendly giant I got the first week. Also an original Vanquisher (first iteration that was for sale)