I've only been twice (and really I'm only counting one) but I think I've established some likely traditions.
1. Never get to the con as early as you think you will on Friday. This tradition is based on everyone you're carpooling with having catastrophes with their costumes, supplies, etc...
2. Spend way too much time aimlessly wandering the halls, looking at cool cosplays, posing, or trying to sit on The Thrones, rather than actually doing anything or going to panels. (I spend the vast majority of con-time doing this, I think...)
3. Always Buy Mochi.
4. Always have some serious issues with your makeup/prosthetics. >O (I hope this doesn't become a tradition but the past two years I had massive issues with liquid latex, face putty, etc.)
5. Go to your hotel room completely exhausted feeling like you want to just hit the bed and pass out; stay up three hours more waiting for the shower, watching FMA. (This is probably only gonna be a tradition for me, because I can't help but choose cosplays that are so makeup-intensive that I CANNOT DO MORNING SHOWERS.)
6. Always look for THAT ONE COSPLAY that you know full well you will NEVER SEE -- but if you stop looking for it in the halls, it'll turn out it was TOTALLY THERE and you just MISSED it.
And a tradition I have not yet taken part in but really want to:
7. Make Hotel Bacon and Hotel Oatmeal. (Oatmeal made in the coffee pot, bacon made by wrapping it fully in aluminum foil and ironing it till it's cooked.)