Hi,

You can totally wear a sports bra with no shirt, BUT you have to wear a number on your front side while you run.  If you want to go shirtless, then you'll need to purchase a race belt that you can put on before you run.  I'm sure the Sports Basement tent will have one you can buy for around $6-$10 tomorrow morning.

You can wear whatever you want under your wetsuit!!  :)  I recommend tri shorts and your sports bra/shirt.

Good luck tomorrow!!!!!