GORP has this great article with five tips for having a more enjoyable time on the trail. That burden on your back can get uncomfortable several miles down the trail. These tips will help a lot.
clipped from gorp.away.com

Gravity’s Drag

Pin a stuffbag inside the pack to stop dense items from
gravitating downward

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.

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