I have been invited to a black tie event at the end of January. I have bought a black dinner suit, bow tie and black braces. I was going to buy a black silk cummerband but am not sure whether you should wear the cummerband with braces or not. Is it both or one of the other? Also, should I wear a waistcoat? Thank you.
The cummerbund has nothing to do with braces: it is not to keep your trousers up. It is there to give a neat visual transition between the top of your trousers and your shirt. You wear it whether you use braces or not.
I go to around 20 black tie events a year - I have worn a black bow tie and matching cumberband once - all the others I wore different colour bow ties and even a white jacket (though this shouldn't be worn in this country - really only in hotter climates) with blackdress shirt and white tie,
I wouldn't wear a waistcoat, but have worn braces plenty of times - with and without cummberbands.
Go in what ever you feel comfortable in - but if you are in doubt simply wearing just a black tie is safe - all extras are trimmings (and style)
As said, the braces are to hold up your trousers. The cummerbund is merely ornamental !.But you wear either a waistcoat or a cummerbund, not both.(It's fine not to bother with either the cummerbund or a waistcoat, but most people wear one or the other because that looks better, a bit more fancy).