The AD&D Second Edition Player's Handbook, I'm fairly certain, was the first D&D product I bought.
Or maybe it was a set of polyhedral dice?
I know it couldn't have been some Ral Partha miniatures, those came later.
For the first couple years I DMed, my brother loaned me his AD&D First Edition books. Just the corebooks and couple of adventures like the Sinister Secret of Saltmarsh, not stuff like Unearthed Arcana or the Wilderness Survival Guide. So I held off on buying AD&D 2e stuff for awhile.
When did I switch my Greyhawk Campaign to AD&D Second Edition--late 7th Grade, maybe?
I still have that AD&D 2e Player's Handbook I bought all of those years ago. It got a lot of use--the binding and threading is starting to give way. But that's why I bought another copy a few years ago.