i am not that much of a downhill only rider but i do know it is an essential part of riding. you will need full helmet, body armor, shin protection and nice gloves. i would recommend fox and sixsixone.
I rode with flats for a while but I recently purchased some hybrid clip pedals. i have really enjoyed these and would not go out to the tail without being clipped in. the hybrid makes it great if you want to just mess around and not worry about your shoes. but now going through those technical sections you don’t have to worry about your feet slipping. i would highly recommend going clippless if you have not yet, but make sure you practice before hitting the trails.