If you're going out costuming, and don't wanna worry about the potty, I suggest dehydrating yourself before heading out. It will eliminate the need to pee. Stop drinking liquids a few hours before you go out, and if you do drink, limit your intake to small sips.
Fortunately anyone in big costumes with lots of armor, they are often very hot to wear, so you'll be sweating like crazy anyway, so you're less likely going to need to pee.