The first module I ran was B2: Keep on the Borderlands.
Because it came packed in the Basic set that I got for Christmas '80. So that's what we started with. A few days after unwrapping the best Christmas present ever, a party of 2 elves, a 1/2ling, & a fighter found themselves trudging up the road to the Keep. And shortly after that, armed with a few rumors (& all the weapons they could afford/carry), they began exploring the Caves of Chaos.
They picked a cave at random & brought death & destruction to the Goblin lair. And the ogre. And the Hobgoblins. And the....
We spent most of '81 playing through B2. We were kids though, so sometimes we'd play a lot, sometimes a little, and game sessions could be spaced out anywhere from several days to a month or so in-between.
The party also changed frequently as the players tried out all the classes. But every few sessions the players would come back to running those initial characters.
The first module I
bought would be X1: The Isle of Dread.
Because it came packed in the Expert set that I bought in the spring of '82.

By this time I was getting better at adding story to the game, so when the players beat the undead temple in B2 I had them find a "Treasure Map" as part of the loot. The evil priests had found the fabled "Isle of Dread"....
Pick your characters, level them up to 4th lv using this new book I got, & next time we'll be off to The Isle of Dread!
Several weeks later 2 elves, 1 Halfling, & 1 fighter set sail.
After that I have no idea what order we bought/played stuff, except that summer during Isle of Dread we started adding 1e stuff. Eventually the game switched to 1e using a combination of BECmi modules, AD&D modules, Judges Guild & Dragon stuff, & stuff of our own. Mid-'82 - '89 we played alot & often.
