Buying a rucksack
There are plenty of adventure shops selling rucksacks.
You should look for a size that is going to accommodate all the gear that you will need on your trip. A 65 litre bag is about average.
A wide range of rucksacks are available online through Gear Zone.
Buy rucksacks online
Look for a padded hip belt. This will take the weight off your back when trudging around town looking for a place to stay as well as during any hikes you do. You should aim to carry about 50% of the weight on this belt. (At airports wrap the hip belt back around the pack to ensure that it doesn't get caught in the conveyor belt. This will also help deter or slow down nosey people.)
Waterproof rucksacks?
Very few bags are totally waterproof and it is not really worth your money spending the extra on this. As well as using plastic bags to keep your clothes dry you can also buy a waterproof cover which can be attached to most bags within seconds for those inevitable downpours!
Customise your new rucksack
It is worth customising your bag with a badge or souvenir of some sort to keep it easily recognisable to you at airports and to also show others they have the wrong bag.
Where to buy good quality rucksacks:
GearZone
Gear Zone has a wide selection of backpacks, rucksacks, day sacks and travel bags for first-time backpackers as well as the experienced traveller wanting to upgrade.
Next: Insure your belongings