Yes to all of these! I've tried to bring my fantasies to life as much as possible:
Christina - I dressed as her for Halloween once, but unfortunately not the Lady Marmalade outfit. This was my first time dressed in front of muggles. Quite a few years later, I lipsynched to an Christina song for a charity drag show, but again a different outfit. I also did a Lady Gaga number for another drag show. Drag shows are a great way to feel like a female pop star for a few minutes.
Cheerleader - I bought an authentic cheer uniform, learned about the sport from cheer web sites, and then learned some basic cheer dances from online videos. I did a a cheerleader photoshoot and even got some outdoor pics in the outfit. I went to a Halloween party in the same outfit last year.
Ballerina - I simply adore tutus. I love the way they bounce as you jump and spin. I was fortunate enough to be given a collection of tutus by a CD friend who was making room in her closet. I've been taking ballet lessons for years now, and although I present as a male in class, I always wear tights and I'm in a very feminine space in my head. I've done a couple of photoshoots in my tutus, and have used my ballet knowledge to achieve authentic poses. I would love to join Les Ballet Trockadero.
Showgirl - Please see my story in the "Special Events and Occasions" section for my attempt to live out this fantasy.
I find it interesting that when I go out to CD events, I try to dress classy, and (the CD side of) my closet is mostly filled with nice dresses and skirts. Yet, I still find this strong urge for these fantasies. I wonder if that's in part because I never had the opportunity to try on these role when I was young, like ordinary girls did, so I'm making up for lost time.