The backpack should fit well, so finding a sport shop to measure you for the right size is the first step, particularly if you want an internal frame pack.

The gear you need to take should fit in the pack, so you need to have an idea of what you have (or what you will need to get) in the way of gear, how much it weighs, how much space it takes, etc. You need to find out if you need a bear canister in the hiking destinations you plan to head out into, and take that into consideration as well as some canisters don't fit well in some models of backpack.

some articles:
http://www.trailspace.com/gear/guide/backpacks.html
http://www.rei.com/expertadvice/articles/backpack.html

Do you have gear already? and finally, what does hemp have to do with it?
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"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

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