OK, the Camelbak Mule NV Hydration Pack is not massive(12L + 3L reservoir), so if you’re planning on taking your entire wardrobe, this one is not for you. It is a great size to take a decent amount into the arena each day though, and designed for all-day comfort in extreme sporting situations so it should withstand your shenanigans.
The NV back panel is designed to help the weight settle more comfortably on your lower back and the pods provide ventilation, so less sweaty backs. There’s a handy integrated rain cover. Always useful. Helmet hooks, and plenty of accessible pockets for, you know, man things.