The first thing to remember when packing for a long trip is to travel as light as possible.Remember that you may have to carry your backpack around for long periods, also, you may wish to buy things on your travels. Campsites have washing machines, so there is no need to carry a month's supply of clothes.

Backpacks-
50 litres for women,
60 litres for men,
plus a day sack

To make things easier on yourself when searching for things you've packed into your backpack,seperate your luggage into see through bags.Zip lock plastic bags are especially good.

Also,bring plastic bags for dirty laundry, as well as for shower gels and shampoos,etc (These may spill in your bag).

Clothes

Bring light-coloured, lightweight clothes, made from material that doesn't sweat or need ironing. Roll your luggage, it makes them easier to pack an helps prevent creasing. Bring one pair of good pants/jeans for going out as well as two tops.Don't bring anymore than this. Cargo pants that zip off at the knee are ideal for travelling, especially to hot countries. Bring a special microfibre travel towel as they are more practical than normal towels.Most specialist stores have them.

Footwear

Bring Hiking boots, sandals, and flip flops(for showers in camp sites) Also bring plenty of underwear and socks.

Other Essentials

-sunglasses
-hat
-sun cream
-firstaid kit(see below)
-passport*
-travel insurance
-credit card and bank cards**
-universal bath plug
-padlock and chain(for backpack)
-pen and notepad(journal and addresses)
-document folder for papers, photocopies, etc
-alarm clock
-pack of cards
-book
-swiss army knife
-mini maglite torch
-elasticised washing line

First-aid kit

-aspirin or paracetamol
-antihistamine-allergies,bites and stings,motion sickness
-throat lozenges
-lip balm
-antifungal cream/powder
-water purification tablets or iodine
-thermometer
-multivitamins
-insect repellent
-arret(or something else for diorreaha)

*Bring 2 black and white copies of passport. They must be sharp and clear. keep one in your backpack or luggage and another in your daypack. You should also leave one at home with your parents for example, or alternatively you scan it and send it to your e-mail, meaning you have access to a copy wherever you are in the world.

**Also take down seperately the number of the credit card(s) and where to phone if you lose them.You should also let the credit card company know that you're travelling as they may shut off the account if they detect abnormal activity, such as spending more than normal