Don't purge. You'll just regret it in the long run. Especially if you find yourself single again.
What to do really depends on your situation. If there is a good chance that your relationship is going to be long-term, it's better to come out to your girlfriend earlier rather than later.
If you don't feel comfortable doing that, rent a storage unit in your name only. It's also a good place to stash any furniture or other items you want to keep, but don't have room for.
Depending on your need to dress, you can keep a carpet-bag or small piece of luggage containing one or two outfits and any makeup or accessories in your car. Make sure you have a luggage lock on it though. If your gf asks about it, you can just say it's a change of clothes.
Finally, stick to wearing your own outfits. Don't succumb to the temptation to wear your gf's clothes without permission.
Realistically, if she can't accept you as you are now, it's not going to get better in the future. Remember that you are keeping a major fact about yourself from her, and that lack of trust will hurt when/if she finds out.