Just to clarify, you're an MTF who is on hormones and wants to pass as male for safety reasons?
Obviously some things here aren't going to apply to you, such as name changes, and all that social stuff, but I suppose our information on binding might be useful. If you've only got small breasts (I don't know if you've had surgery there or whatever) then you might get away with just not wearing a bra at all and having a layer or two on, but you'd probably be more comfortable with a sports bra on at least, and although I've never tried it I've heard a lot of people say that they work for smaller breasts, as long as you get the ones designed to compress and not enhance your breast appearance.
For larger breasts you'd probably want to look into getting a binder, it really just depends on what you're having to wear and what the climate is. I don't bind at all at the moment as its' winter and I wear a few layers, but if I had more up there, or it was summer I would be constantly binding.
Haircuts all depend on which aspect is more important for you, but you can get some nice andro short hair styles if that interests you.