Louise Young brushes are amazing, especially the round foundation brush.
I have at least 6 MAC 217's as they are so versatile.
White Face & Body foundation from MAC is essential, cannot live without it. Great to mix into other foundations.
Benefit High Beam gets used on most brides, especially on the décolleté.
Have at least 2 different types of foundation, primer & moisturiser for different skin types.
Tit tape is very handy to have along with all the other random stuff already mentioned.
Makeup Forever Mist & Fix is fab for setting make-up, love it.
Layer blusher, cream first then powder on top, lasts longer and looks great.
Always give the photographer your business card and ask them for an image for your portfolio (don't forget to get the Brides permission to use it).
Keep a disposable set of brushes handy just in case one of the bridesmaids has a really bad skin condition that I don't want contaminating my own brushes. The Pro Make-up Shop do a great set.
Chanel do a great Brow set with 3 different colour powders.
You will be photographed a lot if the Bride has asked her photographer to be there while she is getting ready so make sure you have painted fingernails and clean hair. Keep your own make-up, jewellery and perfume to a minimum.
Never be late - ever.
I could keep on going but I've got to go to work now!