A couple of years back I did this detailed write up of the AD&D games I played with Gary Gygax back in the 80s, because a couple of folks requested it, and as I get farther away from the event (now almost 30 years ago...) my memories are more likely to fade.
Note: these posts contain some spoilers for Gary Gygax's adventure Necropolis
Glathricon was the local gaming con in Evansville, Indiana, where I grew up. In 1987 and 1988 Gary Gygax was the Guest of Honor. In 1987 I was 12 years old and went to the con with a friend, my second time at a con after going to ConTact (the local SF con, which also had some gaming) the previous fall with my dad. I'd broken my arm a couple weeks before the con so my arm was in a cast. One of the con organizers saw me wandering around and asked if I'd like to have Gary Gygax sign my cast. They led me into the banquet room, where Gary was in the middle of his dinner, and told him the situation, and he graciously agreed to interrupt his meal to autograph my cast. That was my first encounter with him.
By the next year I was 13, had been playing D&D for a little over 4 years, and - as 13 year-olds tend to do, had a pretty high opinion of myself. I considered myself pretty much an expert on D&D, had a subscription to Dragon magazine, and was starting to branch out into other, non-TSR games. I was also getting into exploring D&D from before I'd gotten into it (I had the various Best of Dragon volumes, and had bought the OD&D Supplements from TSR's Mail Order Hobby Shop) and had become a fan of "old school" D&D and thought TSR's recent stuff (Dragonlance, Forgotten Realms, etc.) wasn't up to the level of their old stuff. I went back to the con along with a different friend from the previous year, John, my best gaming buddy.
On the Friday evening session we decided to forgo the RPGA events (which we'd already figured out tended to be kind of lame and dominated by hammy-acting players) and instead play one of the New Infinities events (New Infinities was Gary's post-TSR company, and they brought pretty much their whole crew down to Glathricon both years). A dozen or so folks were gathered in the staging area, and the organizer asked "who here hates elves?" and about half the people, including my friend John, raised their hands, and were led off to their table. They ended up playing an adventure called "Those Darn Dwarves!" which was apparently a comedy-module and my friend said it sucked. Left behind were me and 3 other guys - all male, all teenagers a couple years older than me. I'd never met any of them before and don't remember any of their names. Two of them were friends, the third was a loner, like me. The organizer told us to hang tight that we were in for something special, and that Frank Mentzer was going to be along in a moment to tell us about it. We all got very excited and started speculating what we were in for.
He showed up shortly, and told us that we were going to be playtesting Gary Gygax's new adventure, with Gary himself, but that we first needed to roll up characters. He gave us directions that were very loose - pretty much we were told to generate high level characters with whatever stats we wanted, because this adventure was going to be really tough and if we made bad decisions high stats weren't going to help. I can't remember if we were given a limit on levels or magic items. I rolled up a 20th level (IIRC) thief. One of the other guys made a magic-user, another made either a fighter or cavalier, and the 4th I think made another fighter (amusingly, no cleric).
A half hour or so later Frank came back, gathered us up (maybe looked over our characters? I don't think he did), and led us upstairs into the banquet room where the gaming tables were set up - I could see my friend John at one of the tables nearby - and led us to where Gary was waiting. I waved at John to get his attention and we both made shocked expressions at each other. Since we had a small group we were all seated around a round table. Gary didn't use a DM screen and I don't think he had any rulebooks, but he did have his dice and his smokes (unfiltered Camels, which he pretty much chain-smoked non-stop), and a thick sheaf of typed pages and hand-drawn maps, held together with one of those metal binder-clips.
He was extremely friendly and engaging right from the start. He greeted us and told us he was going to be running his new adventure for us, that it was called Necropolis and was the toughest adventure he'd ever written. He quickly went over a few new rules that we'd be using - Joss, the BUC system of currency, and that a rolled 20 attack means max damage - and then gave us a choice of what we'd rather play - something action-heavy, or something based more on problem-solving. We all voted for the latter. Gary showed us the map of the adventure we chose not to play (the Temple of Osiris section of Necropolis) and told us a brief summary of how that adventure would have gone - that if we'd succeeded at it our reward would've been winning permission to explore the tomb, which is what we were going to be playing.
He then gave us some background and overview of the Egyptian-flavored setting of the adventure and showed us the map of the village of Aartuat, told us that it was pretty much like Hommlet to the tomb's Temple of Elemental Evil, and that there was a merchant there who sold "lucky" statuettes of the Egyptian gods that we might want to purchase. This morphed into a quick roleplaying scene with that merchant where we picked out which statuettes we wanted. On the merchant's recommendation I bought a statuette of the god Bes; IIRC each of the others also bought statuettes, but I don't remember of which gods (probably the usual - Osiris, Anubis, etc.) and then we were off to the tomb...