Ah, Cosplay. Very few human endeavours give one the dubious pleasure of tearing up and down hotel hallways at 3:00 am screaming “DOES ANYONE HAVE A MEDIUM SAFETY PIN?!?!”
If you’re a serious costumer, nothing I can say here will do you any more good than give you a soft chuckle of recognition. For the rest of you, plan on building a kit around one of those travel sewing kits, including bits and bobs for touching up your costume. Buttons, glitter and/or sparkles, polish for the metal bits… if you used it during construction, plan on bringing at least some of it in the emergency kit. If you’ve got a bit of room to spare and an industrial bent, bring a hot glue gun, the mainstay of emergency costume repair. Having that extra safety pin at 3am can earn you a new friend.