The day I went full-time at work, because I knew I'd never have to pretend to be a guy again.
I did keep some denim shorts for yardwork, and I love my flannel shirts so I saved those (but around here plenty of women wear them too, so I figured it's more "unisex" than male clothing). Oh, and socks. Men's socks keep my feet a lot warmer at night.

My wife also rescued a few items and now she wears them.
Of course, a few years later and the closet is stuffed to the gills again anyway... go figure!