1) "Have you eaten lately?" is always, always, always a reasonable question to ask me at a con. I'm doing better than I did at my first cons, where I invariably gave myself crashing headaches and sometimes made myself dizzy losing track of time and/or trying to stretch things "just one more reading/panel/conversation." But still, it never hurts to ask, and it sometimes helps. Also, I am a morning person, so if you're meeting up with people for breakfast, hey, I'm people.
2) I will have bars. If there are any left by the time you find me, you may have one. Unless there's only one left and stillsostrange hasn't had any yet, in which case it will be the Reserved Bar. I may try to press bars upon you, although I will try to remember if you've said you have a gluten allergy or are eating low-carb or something like that, so I can refrain from tormenting you.
3) If I have a thicker Minnesota accent than you expected, I am probably uncomfortable in some way. Nervous and tired are the best bets. The exception is the sentence, "Have a bar," which is permanently Minnesotan. Also, I say "yah" more often than "yeah" or "yes." Do not be alarmed by the yah.
I am not actually an extrovert. I just play one at cons. Being around new people and/or lots of people makes me nervous and takes energy. It is nothing personal, I promise.
4) If you startle me, I will become terse and reticent while dealing with whatever startling thing you just said. This does not mean I don't like you.
5) I have never once bitten someone's head off for recognizing me from online at a con. If I've never seen you before and you see me, come say hi. This applies particularly if you don't have a picture for an lj icon. I will be squinting at people's badges, but if your username is not related to your actual name, this may not help. Just say hi, tell me who you are. I'm friendly. (I mean, I'll have bars; how much friendlier does it get?)
Maybe this will be the con where nobody new recognizes me from my backside. I doubt it, though; it's never happened before.