So you want to go backpacking? Great! You'll need a decent travel backpack though. This guide will help you pick out a good one that'll stay in one piece for the whole trip.
Type of travel backpack
There are two main types: wheeled and non-wheeled. The one you go with depends on what your destination is going to be. If you are travelling in largely urban destinations, or developed countries, such as a tour of Europe, you might find a wheeled backpack is the way to go, especially if you plan on carrying a huge load of stuff. The wheels take the pressure off your back, allowing you to pull it along the pavement or road by its handle. However, if you're going to some more off-the-beaten-track destinations, such as South East Asia, wheels are not such a good idea. Uneven pavements, potholes and muddy tracks will soon clog your wheels and make your travel life hell! A possible compromise is to purchase a travel backpack that can be carried both on your back and pulled along the ground - Victorinox sell these, for example - but these may cost more.
What size backpack?
This is the ultimate question. What size should you bring? Generally speaking, the smaller, the better. It all depends on how much stuff you intend to bring. I would suggest that a sensible size to aim for is around 65 litres. This is large enough to give you some space, especially for things you may pick up along the way such as souvenirs, but not too unwieldy so that you will look like a member of the Special Forces lugging a bergen about town. The smaller your travel backpack, the easier it will be to stash it on trains, in the compartments under buses, and in taxis. The bigger it is, the more trouble you will have with such things. Also the bigger it is, the more likely you will fill it with useless rubbish, and the heavier it will get. Do yourself a favour in advance and only get a medium size.
Do brands matter?
So you want a North Face Backpack? I'm sure it will look nice on you. But don't get carried away with brands. Most backpacks you'll see in the shops will do a perfectly decent job for you on your months-long (or yearlong) journey around the world.
Pretty much the only vital accessory you're going to need for your travel backpack is a raincover. It's absolutely imperative it has one. It's most likely tucked away in the bottom of the pack, in a secret or concealed pocket. The moment it chucks down with rain on your journey, make sure you cover up your pack; most are not fully waterproof and so the rain will slowly seep through the tough fabric, settling in the bottom and making your clothes damp if you are lucky, and destroying any electronics within via water damage should you be unlucky. Everything else - zips, straps, carabiners and the like - is much of a muchness between models. So-called "back-cooling systems" can admittedly be of some use - the idea is they allow a gap between your spine and the bag for airflow and to stop it getting sweaty - but they aren't essential.
Choosing a good travel backpack is an important part of preparing to go travelling. Try to see them in person first; don't just order something off the internet before trying it on and getting a "feel" for it. It'll be strapped to your back for the next few months; make sure it's comfy!