Panties. The name in and of itself brings on a sense of disgust that I can't really explain nor justify. I've never called them that, beyond that one time just then. To me they're undies or underwear. I wore boys briefs as a kid, though changed to girls briefs during puberty for some reason. I moved with my mother then, so that's probably why. My first transition step was to purchase boxer briefs. Can't believe I didn't start wearing them earlier, they're so much more comfortable!
As for bras, I can deal with them. To me they're just another form of clothing. It's more uncomfortable to not wear one, as such I generally sleep with one on (a loose one). I don't wear them when binding though, only because my binder does a better job at keeping my chest in one place.