I want to say from the off that the most important thing about the wedding day emergency kit is that you should not be the one not carrying it! Nonetheless these are the essential items I would recommend having before you head out for your big day. Tissues - Every bride/groom handles the wedding day differently, some hold it together others are genuinely overwhelmed with emotion at the sight of so many family and friends. So it's perfectly normal if there are a few tears (I can still hear my make up artist sister saying 'if you need to shed a tear, tilt your head back...save the make up!!') however it's always handy to have a couple of kleenex to hand just in case you get a few runners!
Make up - Potential tears? Sweats? Genuine wear and tear throughout the day? It's definitely handy to have any essential items of make up that you may need during the day with one of your bridesmaids; eyeliner, bronzer, lipstick of choice (definitely a must if you have gone for a bold colour) just so you can have a touch up and feel radiant for the whole day...though if you're having such an amazing time that you forget to touch up, I won't blame you for that either.
Perfume - It's usually a long day so as much as you will have prepared a liberal dousing before you head out the door, you should pick up a mini perfume atomiser to savour a bit of your wedding day scent, particularly useful at regular intervals like just before the reception drinks post wedding and before the night time festivities kick off; you'll be smelling sweet all day and it will really help solidify the scent memory - I even blogged about the nostalgia surrounding smells and how they link back to memories, check that out here
Plasters - You are wearing a pair of shoes you probably haven't worn for more than 15 mins at a time (maybe longer if you have tried to break them in whilst striking the balance of keeping them looking pristine brand new) it's a good idea to have a variety of plasters to hand just in case after an hour you begin to regret the decision of those being 'the one'. Even flats and sandals can lull you into a false sense of security of being comfortable...definitely better to be safe than sorry on this one! I know it's common to throw 3 sheets to the wind by the evening reception and go foot loose and fancy free sans shoes, but this tip might be helpful until that point!
What emergency kit supplies did you have that would you suggest for other brides?