Packs used for traveling are a bit different from packs used for hiking -- they tend to be larger, heavier, and sturdier. This is because they need to withstand being tossed around by airport baggage handlers. They are often quite large because they have to hold all the travelers goods.
On the other hand, the packs used for hiking can be smaller and lighter. Backpackers carry less weight than most travelers, and they handle their packs a lot more gently. A lot depends on the length of your backpacking trips. A good weekender pack will probably not work as well for a ten day expedition.
Much also depends on whether you're travelling alone or in a group. When you travel in a group, each person ends up carrying a bit less weight. Another factor for longer trips is how frequently you'll be able to resupply.
If you're hiking a section of the Appalachian Trail, it's pretty easy to get into town from almost any major road crossing, and you cross major roads every couple of days. On the other hand, if you're in the middle of the northern Ontario wilderness, resupplying can pose considerable logistical problems, and you may be forced to carry a lot more food with you even for shorter trips. It is also worth your while to discuss your needs with your local outfitter.
Most of the better outfitters can give you excellent advice -- the folks who work at such places are experienced backpackers who have actually field tested the stuff they sell. Read the reviews in the major outdoor magazines, like Backpacker and Outside! Once you have determined your needs, you can choose from a fairly broad range of high quality brands. I will give you a short list of the better brands -- for the most part, these companies categorize there packs according to type (internal frame vs external frame) and intended use. Do your research, and then browse through the list. Word of advice: The packs designed for longer trips (7 - 10 days, e.
g.) are designed to carry all the supplies that you'd need for a trip of that length. If you'll be able to resupply every 2 or 3 days, then you'll only need a pack good for 2-3 days. There are many long-distance hikers who go with ultra light equipment, carrying no more than 20 lbs in a very light and relatively small pack (less than a pound, around 2400 cubic inches). But it takes pretty specialized equipment to go the ultra light route, and it's difficult to pull it off in cooler weather because of the bulk of the warmer clothes that you'll need. And even a 2400 cubic inch pack will be larger than you'll need for most day hikes.
A lot also depends on the kind of day hiking and long weekend trips you have in mind. A day hike in the White Mountains or the High Peaks of the Adirondacks will require more equipment than a trip in lower elevations where you're less likely to run into extremes of weather and temperature over the course of the day. Use a small fanny pack for day hikes in the NY-NJ region, but in the higher elevations of New England and the Adirondacks, use a 2000 cubic inch pack to carry the warmer clothes you will need as you ascend to the higher elevations.
And for 3-4 day hikes,use a frame pack (6+ lbs, 5000+ cubic inches) and carry enough amenities to make a comfortable camp. On the other hand, when you are out for 8-10 days of Appalachian Trail hiking, use a smaller ultra light pack (1.5 lbs, 3400+ cubic inches) and skimp on some of the camp comforts in favor of making hiking as comfortable as possible.
Victor Epand is an expert consultant for http://www.CombatCloth.info/. CombatCloth.info carries the best selection of combat clothing, gear, and accessories on the market.