6. Don't wear heavy costumes in the registration line

This goes back to point #5, heat stroke and dehydration are no fun and will ruin your convention experience. It gets really hot outside and that registration line can take hours to get through. During that time you really don't want to bake inside your costume (plus you probably won't smell too hot afterwards). There's plenty of time, once you get your badge, to go back to the hotel and put your costume on.