So, you’ve toted the backpack around the department store, filled with would-be gear. You’ve strapped, buckled and tightened it to perfection; decided you were perfect for each other, giggled with delight, and brought it home. Now, it’s a few days—or, if you’re anything like me, the night—before your first big trip, and it’s time to replicate the perfect stuff technique you experienced back at the store.
Start by spreading your gear out before you. There’s no rule for what to bring, especially considering the changing seasons, but the old less is more maxim generally applies. You want to roughly separate things according to category, so as not to leave anything behind: Clothing, food, cooking ware, tent, sleeping bag, compass, map, etc. If you’ve gotten to this point, we assume you’ve got a decent idea—or friends who do, at least—of what you’ll need.
Here is the central rule around which you want to pack your stuff: Heaviest items closest to your back, and nearest the middle-bottom of the center compartment. The key here is to not be top-heavy, and to hug the heft close to your hips. On steeper terrain, you'll want to move the bulk lower in order to help keep your center of gravity closer to the ground.
If you’re pack is up-to-date, and thus fairly waterproof, skip the following tip (though it doesn’t hurt to take the extra precaution, especially on long trips through unpredictable climates). Line your main compartment with a garbage bag, or some other waterproof fabric. Anything you want to keep dry (food, clothes, and sleeping bag) should go inside. Top this with tents, tarps, rain gear—whatever can withstand getting wet. Alternatively, you can subdivide the contents of your main compartment among waterproof dry bags and compression sacks.
Many packs come with a bottom pocket or separated compartment for your sleeping bag; if you have one, use it, since extended stays of compression compromise the sleeping sack’s loft, and therefore its warmth.
Anything fragile, or metal, for that matter— and don’t forget that the hollow of a pan is extra space, too—should be wrapped or surrounded with softer materials like clothing. This protects them from rattling around or breaking.
Keep stove fuel separated from your food, in case of accidental spillage.
Any items you want readily available on the go should be stored in the top pocket—aka "brain"—for easy access (or side pockets, if you have them). These items include, but are not limited to, a multitool, hand-sanitizer, headlamp, camera, map, compass, phone and a light snack. Most brains are waterproof, but check before risking valuables. If yours isn't, you can store items in Ziplocs to protect them from moisture. Many bags also have waist pockets in the hipbelt for storing snacks and on-trail goods. Some people attach water bottles to their shoulder straps, but it's often more convenient to use a Camelbak-style hydration bladder, which is tucked into an internal sleeve and its hose threaded down the shoulder strap. Water bottles, after all, knock against you when they're jostled, and often require you to stop moving to take a drink.
If you have external loops, use them for shovels, ice axes, and other clunky items that can puncture the interior. If sharp objects must go inside, blunt their edges by wrapping them with an article of clothing. The most important item to have readily available—at least when traveling in bear country—is bear spray, which is typically belted to a shoulder strap. As far as strapping things to the outside of your pack goes, it's best to keep everything as tightly attached as possible and not dangling, so as not to become snagged on surrounding flora.
Remember that the weight distribution game works not only vertically, but also horizontally. Try to apportion the left and right with equal weight.
These are only rough guidelines to help you pack for a comfortable, enjoyable journey into the wilderness. But remember that the great beauty of modern backpacks lies in their impressive adaptability. If we've neglected a particularly head-scratching problem—and with all of the tricked-out packs available today, that's not doubt the case— just remember that as long as you minimize unused space and keep your load snug to your hips and back, the rest is really just personal preference. A little real-world experimentation will quickly tell you what works and what doesn't, and you'll develop a system that matches your gear needs and personal taste.
Finally, stay organized. Elect a wise home for each item, and rarely relocate. The faster that muscle memory sets in, the quicker you can get to what you need. After all, what’s the use in making a system if you have to fumble and fish every time you want to access something. A pack, after all, is only as good as its packer.