I often put a small bag in my GHB for added storage capacity, especially now that it's cold. It's big enough for a couple of two liter bottles, which I would pull from my trunk or my shelves so that I don't have to stop for water initially, and to maximize any refill stops. I wear it in front and it's profile is low enough that it doesn't restrict movement too much. Not optimal for crawling in the mud, but great for making mileage. I hook it in under my regular straps ad link it with my sternum strap. It also helps balance the load if I'm running ammo-heavy.