There are a number of criteria to consider in selecting a pack--and we need to know more before we can make recommendations:

--How much do you need to put into it? (You've answered this question, so I assume you have all your other gear and have measured what capacity you need for all gear plus a week's food.)

--What is the total weight you will carry (total of pack + all gear including. food, fuel and water)? You need to be sure the pack is rated to carry at least the maximum amount you might want to carry in it, or it will be very uncomfortable.

--Mostly on-trail backpacking, or bushwhacking through lots of brush?

--Your torso measurement? (From the bump on the back of your neck to a line level with the crest of your hip bones--don't try to measure this yourself--get someone else to do it)

Large-volume outdoor stores are not the place to buy a pack. Try to find an EMS or REI or a more specialized backpacking/mountaineering store in your area. Take all your gear (including the equivalent in weight and bulk of a week's food and fuel and a day's water) along and make sure you find a clerk who has lots of experience in fitting packs (don't let them palm you off on the part-time teenage help). Try on lots of different packs so you learn what fits properly and is comfortable for you. Packs are almost as individual as footwear.

Most of the best lighter weight packs are made by small individual entrepreneurs and sold only on the internet. That's where I ended up getting mine. You need to go through the above steps first, though, so you know how the loaded pack should feel and how to adjust it.

Please let us know the answers to the above questions so we can help you better.