Murphy's Law of the Inconvenient Migration of Stuff means that dense items (especially waterbottles, hydration systems, large cameras, and fuel) tend to gravitate to the bottom of your pack, especially when the pack is not full and tightly packed. Those are precisely the items that often need to be handy and whose weight should be up high and close to your back between your shoulder blades for easy carrying.

Here's a simple solution:

Suspend a stuffbag to form a pocket inside the pack at an appropriate height. Attach it with safety pins to the strong internal seam that encircles the top of most packs. That way the pins do not pass through to the outside skin of the pack, and it's usually easy to push the pins through just the binding tape on the seam.

If you use a waterproof stuff sack, such as Outdoor Research Hydroseal bags (various sizes and prices, www.orgear.com), you have extra protection against a leaking bottle or hydration system wetting the pack contents. Just don't put the camera in with the water bottle!