For your first class, don't sweat it. Wear something drawstring at your waist, a comfy athletic t-shirt, and call it good. Once you've tried classes and decide you want to return, we can help you order a gi (at a much more reasonable cost with our wholesale discount).
Remember to trim those nails and leave your jewelry at home. If you have a piercing that you cannot remove (something that, even fully dressed, is still on your extremities where it might be accidentally snagged by a teammate) we will help you tape it down for class.