It is just a small thing, but as far as making sure you have everything for your costume and making sure you put everything on in the right place, I always bring a print out picture of each of my cosplays. I find it helps especially with random accessories like Rinoa's arm ribbon or other things like that. You know, when a character has something on one arm or one leg and if you have a picture you dont have to sit there in the hotel room as you are dressing going "ummmm ok now which arm does this go on?" XD It also helps to have a reference for putting on makeup too XD