Catherine go to REI or another professional backpacking store to get your first pack. There are many great backpacking brands. If your in Front Royal there is a new store across from the movie theater that you can get help from. Plus they would probably love the business.
The best advice is to go get a fitting. There are packs you can buy online that have adjustable attachments but then you have to figure the correct fit for yourself. Most good stores, like REI, have an expert that will be able to help you quickly. While you may pay slightly more for a quality pack it will pay off in more miles and comfort.
Check out Duluth Pack Co. Remember your pack is your life line. This co has been in business since the 1800's and they will have all you need.
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