One of my annual traditions is the selection of a theme song for the Tri Season. I always found it helpful that, when, I was deep into a challenging workout, that I could fire up that go-to-motivational song to inspire me to hold it together and finish strong. With that motivational song playing, it gets you those critical extra few heart beats when doing bike or run intervals and inspires you to pick up your pace while picturing yourself closing in on and passing the competition during the last mile of one of your long runs. Racing can be lonely at times and, especially, iron-distance, can be mentally challenging; therefore, having that go-to inspirational song in your head can remind you of those past workouts which got you ready for race day and inspires you to perform. Personally, at Santa Rosa, with 4 miles to go on the Run and my mind mentally mushed, I started singing, "Don't Stop Me Now" from Queen over and over again which helped me to close on my AG competitor and pass him in the finishing chute.
And, as a bonus, as you collect them over time, you can build a playlist that you can leverage for Training and pre-race while setting yourself up in Transition.