Glad someone mentioned a tank-top and shorts.
I made the mistake of wearing a strapless bathing suit underneath. My toga slipped off my shoulder when I was using the bathroom, and unfortunately my bathing suit did some slipping as well. I was REALLY lucky that one of the brothers saw me coming out of the bathroom and suggested I turn around, go back in, and check my toga.
Also, florists don't charge much for crowns/circlets made of baby's breath or ivy. And they look great
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Pictures from that big Phi Kappa Sigma toga party over the years. In the first picture below, they're waiting for the flatbed truck that went around to all the sororities and picked up the dates. My guess is that current risk management policies do not allow the truck to have the actual operating the champagne punch fountain that it had in the old days.