I competed twice in the Keneyathalon at Raton, finished top ten year one and in second place year two.
Camelbak type arrangement, as you won't want to take the time to handle water bottles. Rifle in your hand. I also carried a Glock. Ran without ear pro on so I could hear the snakes.
I have several small Eagle packs that take a bladder and have Molle in back to attach your web gear.