Welcome to the forums Davina! I hope that you make lots of friends, and we can answer any questions for you.
And something I'd like to address, and this is applicable to all the ladies:
DON'T worry about "passable", concentrate more on "blendable".
On all of my outings in girl mode, I am fortunate to have never had a bad encounter. It isn't because I "pass" . Hell, I'm 6' 1" in bare feet, and my 4" heels do make me stand out, plus, I have a face only a mamma Missouri mule could love. And my preferred scarlet tresses pretty much guarantee I am not going to fade into the background...
That being said, When I'm out and about, I dress like the other women. That means: NO evening gowns and tiaras at Walmart! NO fishnet thigh-hi's, micro-mini and fuck-me-pumps at the supermarket (or the PTA meeting...), unless, of course, you WANT to be made.
Dress appropriate to the other women you see, and you should be fine out in the big bad world. Another point: DO NOT slink or slouch about, as if you are trying to hide. Be proud of your appearance, act as if you belong and people will respond accordingly. OK, a pet peeve: You will NEVER find me in sweat pants and sweatshirt. But girl jeans, capris, shorts, or skirts are fine.
On another forum, there are constant new threads from people who say they were 'clocked' at Target, or Walmart, or Victoria's Secret while in guy mode (sometimes girl mode). And it always comes out that they were acting guilty, or suspicious in their actions, instead of acting like any other shopper.
OK, so you are browsing the lingerie section of your favorite store. BIG DEAL! No one, except you, really cares. Imagine being in the automotive section of the same store, and acting nervous, guilty, and skittish. People might think you were up to no good. Same for the ladies section: just behave normally. No one is going to call the gender police. Unless.... you are drawing attention to yourself by acting weird.
>steps off soap box<
Enjoy the day!