As a girl I always try to co-ordinate what I wear, my preference is for dresses so that makes it a bit easier. But I do like to have matching (or at least co-ordinating) shoes and handbag, my hose should blend with my dress, if I a wearing one my blouse should go with the skirt (or trousers) and jacket. All this is obvious, but like most girls I go a bit further I like my underwear to co-ordinate as well.
I have a couple of sets of matching lingerie and d not wear any of the items "solo" they are only ever worn as sets. But more than that I like to co-ordinate my underwear with my outerwear, so if I a wearing a black or grey dress I will wear a black slip and black panties and bra. Yesterday I had on a lilac turtle neck sweater and jeans, so my choice of underwear was lilac panties (with white lace trim) to match and white bra.
Lingerie is, or at very least should be fun, a little frivolous. The material should be satin or light and filmy, it should be trimmed with lace and bows and even a bit of sparkies. I am sure that for many this is a part of the attraction of cross dressing. Maybe it is because I a only a part time girl, but to me this is part of getting dressed, part of the fun.
As a boy I wear whatever is on the top of the pile