Veteran lurker, still learning though.

So I've noticed that while my mindset is very stoic, my subconscious is not. Especially if I'm in a new environment, I find myself easily surprised/startled/jumpy. I want to be the cool, collected guy who doesn't react, but when I hear a loud noise, someone's behind me on the subway who I don't expect, shit like that, I find myself whirling around to face the direction of the noise.

In terms of steps already taken, I lift regularly, and I meditate, although I'm not very good at it. Working on a boxing gym membership, but working on the money for that first. In the mean time, do any of y'all have any concrete steps you'd recommend I take to get my startle reflex under control and become less jumpy?