While backpacking, you'll be doing a lot of walking around, and you'll want freedom of movement for your hands and arms, to point out beautiful views, try the local cuisine or take photos of memorable locations. To make sure a backpack offers a full range of movement for your hands and arms, try it on at the store and ask a salesclerk if she'll help you weigh it down to simulate the weight of your travel items. Walk around a little bit, swinging your arms every which way to ensure that the luggage offers the range of movement you need.
While backpacking, it's unlikely you'll want to carry around an extra bag or a purse for items like your wallet and your purse. So you'll need to make sure that you have easy access to certain areas of your backpack so you won't have to go digging every single time you want to snap a picture. On the other hand, make sure everything closes securely and the access isn't too easy so you don't get taken advantage of by pickpockets.
Because you'll be carrying the weight of your backpack around for most hours of the day, you'll want to make sure the backpack you select offers adequate back support. Look to see if it has hip and chest belts across the front to help relieve the weight on the top of your back and your shoulders.
Choose a backpack with an internal frame instead of an external frame. External frames are bulkier and don't hug as close to your body. With an internal frame backpack, you'll find it's more comfortable to carry around and that it'll be easier for you to move through crowded spaces with. You can also choose frames for a masculine or feminine body shapes for a better fit.
