MATTHEW KNEALE is a roller, not a folder. Mr. Kneale, the British novelist who wrote ''English Passengers,'' says he has traveled to 83 countries and all seven continents, and he's carried a lot of backpacks. His current bag, rigged with chicken wire and chains to foil slash-and-grab thieves, has just enough space for Mr. Kneale's two or three cameras and several days' worth of carefully packed clothing. ''I find clothes stay in a much better state if they're not folded but tightly rolled up,'' he wrote via e-mail from Tuscany.
Loading the bag is a less precise art. ''Try to imagine what you'll need access to regularly and what you hardly use,'' says Mr. Kneale, ''though however much you try you'll probably end up in the hotel where the power has failed rummaging for the flashlight thing that's stuck right at the bottom.''
Backpacking is meant to be liberating. With your possessions on your back, you can leave cities and cars behind, or simply have your hands free to hold a latte. Yet a poorly fitting or overloaded bag can make a backpacking excursion feel more like a forced march. To enjoy backpacking, you need to follow three principles: choose the correct bag, keep the load light and distribute the weight properly.
Buying the Right Bag
Choose a backpack the way you'd choose a very expensive pair of shoes. You need something that fits perfectly, remains comfortable after hours and weeks of wear, and is appropriate to the occasion. Just as you wouldn't buy plastic sandals for a formal dinner, you shouldn't choose a cheap nylon sack for a monthlong trek through the Lake District of England.
Proper fit should be your first consideration. Most packs have adjustable straps, but if the bag itself is too long or short, no amount of fine-tuning will make it comfortable. ''If you're buying a trekking pack, I'd actually recommend you go to a store and get your torso measured,'' said Jonathan Dorn, executive editor of Backpacker magazine. (You can measure your torso at home by running a tape measure from the large seventh vertebra at the base of your neck to the point on your spine between the tops of your hips.) For comfort, the distance between your pack's shoulder straps and hip belt should be roughly equal to the length of your torso.
Size and design are also important. Backpack capacity is measured in cubic inches or liters; daypacks are usually 2,000 cubic inches (33 liters) or less, while a touring pack of 4,500 to 6,000 cubic inches (75 to 100 liters) can hold enough gear for a month or more. An internal frame is more stable for heavy loads, while an external frame lets air circulate between your back and the pack, a valuable feature for hot climates. You can cram more into a top-loading pack, but a pack with zippered flaps or compartments will allow easier access to your possessions.
Once you've found the right size and design, check for comfort and adjustability. Every backpack feels fine when empty, so stuff potential purchases with clothing and gear before trying them on. Beltlike compression straps, featured on most backpacks, stabilize smaller loads and keep the bag close to your back.
Frequent shifts in weight are also crucial to comfort, so look for a bag with ''load lifters,'' straps that adjust the balance between shoulder and hip. Straps should fit comfortably from collarbone to shoulder blade, and the hip belt should be snug and well padded. Walk around the store, swing your arms and turn your head to ensure that straps don't chafe or pinch. ''Don't get seduced by looks, because comfort is what will keep you wearing and enjoying the pack,'' Mr. Dorn said.
What to Take
The traveler's adage -- estimate what you'll need, then pack half the clothes and twice the money -- is particularly applicable to backpackers, whose fatigue and risk of injury increase with every excess pound. Traveling light means packing only essentials, buying clothes as you go, disposing of useless items, and taking clothes that have more than one purpose. Consider convertible pants that zip off at the knee, swimming trunks that double as shorts, sarongs that serve as skirts, towels, beach blankets and wraps. Quick-drying fabrics are also a boon to the backpacker.
When 24-year-old Mark Hulett left Toronto for a five-month odyssey through Southeast Asia, Australia and New Zealand, his backpack contained everything from long johns to swim suits. Reached in New Zealand four months into the trip, Mr. Hulett reported that he had sent home his long johns, fleece track suit and woolly hat from Nepal and had given away his running shoes in Laos. If he could do it again, he would take less and buy more. ''I could have easily put together a few outfit combinations in Thailand or India or Nepal at a very low cost,'' Mr. Hulett wrote via e-mail.
There are some things no backpacker should be without: laminated copies of passports, plane tickets and contact numbers; a flashlight, a first-aid kit, a water bottle, wool socks, good walking shoes, and a lock to protect the pack and its contents. Beyond that, consider everything optional. ''The lighter you pack, the faster you can travel, the more you can see,'' Mr. Dorn said.
Wrinkles No Matter What
Backpackers divide into two camps: rollers versus folders. ''Clothes were never meant to be rolled,'' Mr. Hulett writes. ''I figure if I take my time folding, it is going to get packed just as tightly as if by rolling.'' Mr. Kneale disagrees. ''I find clothes stay in a much better state if they're not folded but tightly rolled up,'' he writes. Wrinkles are inevitable either way, but rollers might have the edge. You can put elastic bands around rolled T-shirts to compress them further, while items prone to wrinkles can be rolled together and slipped into bags.