A long hot shower--like staying in until-the-hot-water runs-out long shower.
Putting on some sad music and having a good cry. It does make me feel better, in a strange way.
Getting involved in some menial task that takes my mind off things--like a mindless video game, vacuuming, etc.
Going on a drive, putting on some of my favorite music and just rocking out.
If it's something I actually have control over, I'm all into prepping---making lists, mapping routes, rehearsing the event in my mind, leaving early, etc.
If it's something over which you have ZERO control, distraction is the way to go (*look! shiny object!*) but if you do have some modicum of control over it, then prepare, prepare, prepare.