You need a strong and comfortable backpack to carry all your clothing and equipment. Choose the very best you can afford. It should have tough and fully adjustable webbing, well secured to the pack’s frame or fabric. Heavy loads can quickly loosen poorly made webbing. It must have a comfortable hip belt. The secret of wearing a pack is to take the weight securely on the hips – the body’s strongest pivot – not on the shoulders and back, which quickly strain and tire.
Do you want a pack with an external or an internal frame? Internal frames are lighter and make a pack more easy to stow, but external frames are stronger, ensure a more even distribution of the load and are especially useful for awkward or heavy equipment – including, in an emergency, a sick or injured person. A good external frame should carry the pack high up on your body, putting less strain on hips and shoulders, and it should be designed to allow an airspace between the pack and your back to minimize contact perspiration. A frame adds weight and is more prone to snag on rocky projections or branches, making progress through dense vegetation a little more difficult, but its advantages more than compensate.
Finally, choose a pack made from a tough, waterproof fabric, preferably with a lace-up hood inside the main sack to prevent water leaking in and the contents falling out. Side pockets are always useful, but they must have secure zips rather than straps or drawstrings, which do not hold equipment safely.