A nice tank top is appropriate. Make sure your bra straps are not showing! If you are wearing spaghetti straps, wear a strapless bra.
Open-toe shoes are fine during prefs as long as they are classy, nice, and match with the dress you are wearing.
Another thing to wear....deoderant. I'm sure everyone is thinking, "Well, that's a given....." but you'd be surprised. Bring extra deoderant and body spray with you. It gets hot out there and you'll want to have some extra with you just so that you can be more self-assured.
