So you've got your air ticket, had your jabs, and read your guidebook from cover to cover, and the big day of departure on your dream backpacking trip is quickly approaching.  So the question is: what to pack?  If you've never been backpacking before, and have only been on standard holidays and vacations, you might struggle.  It's one thing fill a suitcase for a week in the sun, but another completely to work out what you'll need to keep yourself on the road for an extended period of time, not to mention having to lug it round with you on buses, trains and between hostels.

So what's the secret?

The only certain way of knowing exactly what you need for backpacking comes from having backpacked before, and learning from your mistakes.  After your trip you'll have an appreciation of the items you hardly ever took out of your bag, and won't bring them again.  But that's not an option for first-time backpackers.  So the following rough guidelines have been written for you to consider when piling up your stuff to pack.  Note that people travel very differently: to different climates and different areas of the world at different times of the year, so it's just not possible to give a definitive list of what you personally should be packing.  Instead, pick and choose from the following recommendations as you think they suit you and your trip.

Clothes - your destination and its climate will strongly affect what clothes to pack, but there's one guideline that applies: don't go bringing too many. Enough clothes for a few days - say, four or five - is sufficient. You can launder your clothes easily in hostels, launderettes or by handwashing in a basin or even in the shower! Try to get out of the mindset of packing for vacation and think practically. Sure, three or four pairs of shoes would be nice, but do you really need them all? How about bringing one comfy pair and a sturdier pair for walking or hiking instead? Same with pants/trousers. One pair of combats or strong lightweight trousers is a good idea, perhaps coupled with a pair of shorts for those hot days. But you don't need multiple pairs of jeans. In fact, you don't need jeans at all; they are heavy and take a long time to dry (especially in a tropical climate!).
General Recommendations for travel in a temperate climate: 1 pair trousers/pants, 1 pair shorts, 5 t-shirts, 1 fleece/long sleeved jumper, five pairs of boxer shorts/socks, 1 pair trainers, 1 pair hiking boots.

Gadgets - there are so many backpacking gadgets on the market nowadays you could fill up a whole backpack with them alone!  GPS handhelds, flashlights, wind-up radios, mini laptops, wifi detectors, leathermans, swiss army knives... they're all so tempting, especially to someone eager to be prepared for their first trip who has a few dollars in the bank to spend.  Unfortunately, if you buy them up you'll probably get to the end of your trip finding you rarely used some of them.  I would certainly recommend bringing a cheap digital camera to document to wonderful things you'll see on your travels.  A small flashlight will also come in handy for creeping back into dark dorms at night after an evening on the town.  Some backpackers also bring mp3 players with them to relieve boredom on the long journeys that they'll inevitably be taking.  But to be honest, it's hard to find a persuasive argument for bringing much else (in the way of electronic gadgets, at least).  The more you bring of value, the more chance you have of something of value breaking or being stolen.

Washbag and towel - a travel-size shampoo, and either some soap (in a box) or some travel-size shower gel, deodorant and whatever else you bring to scrub yourself clean are essentials. In terms of towels, a portable sports/travel towel is the best way to go rather than a huge conventional bath towel. Sports towels aren't fun to use but they dry quickly and pack down to a small size in your backpack. Your washbag can also double up as a first aid kit: paracetomol/ibuprofren/aspirin, rehydration sachets, anti-diarrhea tablets, bandaids, antiseptic and any other relevant medicines should be tucked away somewhere to treat those emergency scenarios (and hangovers).

Anything else - there are a few random things that will come in handy on your trip. Aside from a passport!, you'll find a padlock a useful thing to have for lockers and dodgy hostel doors, a small sewing kit, relevant electrical adapters for the plugs in countries you visit.  Plus anything else you can't do without!

Hopefully these thoughts will have given you some ideas on what to pack for you to investigate further.  Packing light is the way to go, as an unwieldy backpack is a burden you don't want to be carrying around all year.  Packing light gives you more freedom - and freedom is the best thing a backpacking trip around the world offers you.