So, remember that shirt you were so awesome about putting on before you sat down to get your make-up and hair done?
It's got a secondary purpose. It's multifunctional. Yeah, that's how awesome this shirt is.
Your On-Set Shirt should also be a little bit big for you. Big enough that you can throw it on easily over whatever other wardrobe you're wearing.
Why is this important? Because, hopefully, at some point, you're going to break for lunch. When you do, you're going to be able to save yourself some hassle by being able to put your "On Set Shirt" on right over your regular wardrobe. I know, so frikkin' genius.
This will stop you from getting food all over yourself, and, therefore, will keep wardrobe happy, and make you look more professional, because you are. Wardrobe and make-up are both in charge of how you look, so making their jobs easier, and less stressful is going to make you look that much better for the final product.
I know, I know. You don't spill food on yourself when you eat. Yeah, yeah. Neither do I. But you know what, it's a good thing I've had that damn shirt on, more than once. Cause sometimes, there's ice cream for dessert.