Nicole:
Be prepared to experiment. Depending on how much "gear" you need to contain, you may need to play with various brands and styles. Women's pantries tend to be very narrow in thee cloths area, as they are meant to cover, not 'hold in place'. The worst feeling is to have undies stretch a little bit and have one or both of the boys slip out and hang down for the rest of the day.
Now I switch from bikini, to hip huger, to boy shorts, to big girl panties. Would love to wear girls thongs, but they just don't work to keep everything in place. I do, however frequently wear a thong-like gaff, with panties covering the gaff. That gives me a very flat front that looks convincing in girl slacks, jeans, dresses and swimwear. Your mileage may differ.
Regards,
Rhonda