I think it was an el cheapo Turnabout Lp of Monteux and Munch conducting Rimsky-Korsakov. Now looking around the 'net I see that they want $12 or $15 for this thing. Sheesh. I think some of these recordings made it to CD on the Munch and Monteux "Concert Hall Recordings" sets that were put out by Disky.
Another one that I got early on from Licorice Pizza was Bernstein conductiong
La Valse,
Bolero and
Daphnis et Chloe Suite No. 2. I didn't know until recently that Bernstein did the whole D&C ballet.

My first CD was years later, and that was Jeffrey Siegel playing Gershwin with Slatkin and St. Louis.

I have that on a Vox Box now, and it is an excellent set and sounds better than that early CD.

However, the first CD that I ever
heard was the original CD release of the Ferrier/Patzak/Walter DLvDE. That was a mind blower. I didn't even realize it was mono at first.