My most useful purchase was breast forms. I have several sets and have one of them on most of the time. But my favorite is the denim skirt I bought a few months ago. It looks great on me, even in (semi-) male mode.
The worst (out of many potential candidates) is a rust colored a-line dress that made me look like a water buffalo. Second worst is anything I bought to look "sexy." That is so not-going-to-happen!
