I have pre-con and during con rituals/superstitions.
Pre-con:
Since Kumoricon 08', the con when I was still recovering from a dislocated knee, I make sure to not practice any anime dances, or things I might get hurt doing, at least two months prior to the con. I managed to recover from another knee dislocation and an ankle dislocation just in time for 09'. So, that ritual is staying.
I of course take like ten showers every day, and use proactive to keep away zits. I also hide my con outfit, so I can make an epic reveal the day of the con and march around my neighborhood and show my neighbors, who await it every year.
I also have to bring a hella lot of medicine and everything for if/when I get so nervous I get really sick.
I marathon animes I cosplay from too, to get in character. I also start acting like the character at all times, I know I'm a loser. xDD;
During-con:
I always lose something VERY valuable at the con, 08' a cellphone, 09' a camera and a chocobo. No matter what I do I lose something or another.
I also manage to hurt myself at the con on a moderately to decently bad level.
At one point or another I have to take a nap on the first day or I'm worried I will miss something or pass out.