I do have two memories from my first 
major gaming convention.  It was Origins when it was in Towson, MD (don't ask me the year, but it was the 80s).  I went with a group of gamers who were running games, and I was running couple.  I couldn't tell you what I was supposed to run, probably champions and maybe D&D.  
I do have two strong memories of this convention.
The first was I was given about 2 hours to prepare for a 
Melanda, Land of Mystery adventure.  Origins had either oversold an event, or else a GM had no-showed at the last minute and they needed a fill in.  I was asked if I could run, and I agreed (not a difficult system when you've played it).  I asked for the adventure, when I was asked if I remembered the playtest.  Well, I hadn't playtested it.  Opps 
It turns out, the complete resources were two maps and a sheet listing what was in the final encounter area.  I remembered the overland map because an artist friend of mine was asked to draw it.  However, I had very little to go on.  I fudged my way through the adventure, and everyone had fun.
However, when we finish I go to the main room where Lee McCormick, one of the games author was running a session with many of his acquaitances (including Ken Rolston, as I remember).  They had never left the main inn.  They had spent 3-4 hours roleplaying and really never got anywhere.  I admit, I don't really game for that, but I would love to have the skills to be able to do that and have a fun, interesting session.
The other thing I remember was sitting in the open gaming room with a couple of friends.  They wanted to play something, so I agreed to run a Melanda adventure off-the-cuff.  So, I gave them a plot hook and sent them on their way.  They started getting into an argument about hunting techniques (IIRC, the characters were a lizardman and an elf).  They went in character for a while, so I got up and walked around to see what was going on.  I came back after a couple of minutes (while keeping an eye on my friends) and still wasn't needed.    During that session, I did manage to walk around the gaming area for probably 5-10 total minutes while they were involved in roleplaying that didn't need a GM.