My favorite tool to get in the zone is Brain.fm.
This app produces computer-generated “music” that helps you get in a certain state. Supposedly there is some science behind it, but I don’t have the expertise to judge the soundness of the science.
What I can tell you is that the generated sound can replace distracting environmental sounds, particularly if you listen with in-ear earphones.
So next time you need to focus, check out Brain.fm.