Every trekker has their own view of what to carry, and how to carry it - such that it borders on obsession with many enthusiasts. There is no universal right or wrong list or method. Your choice of gear will depend upon your destination, personal experience, your budget and whether or not you are going to have to carry it or rely on porters. The vast majority of trekking routes take you through a wide range of climatic and terrain conditions, so tailor your gear accordingly. Consider also, that if you are not backpacking or tea house trekking, porters or pack animals will be carrying your gear. The latter are notorious for ignoring the frailties of camera equipment and other fragile items, so choose strong kit bags and pack them carefully.
Choose a big one - a large bag half full will carry better than a small one stuffed to the brim with your excess gear tied onto the outside. Be sure it fits you correctly.
Fabric boots are light and comfortable, but not waterproof, offer less ankle support and are less durable than leather boots. Well broken-in leather boots are best - choose a pair with minimum stitching on the uppers and keep them waxed.
Choose your socks carefully
It's worth paying a bit more for good quality ones designed for your particular purpose and the environment you're likely to encounter.
Essential for snow and conversely, wet jungles.
For use in camp and wading rivers
Save your knees a lot of punishment on descents, especially if you're carrying a heavy pack.
Down is still, weight for weight, 100% more efficient than the best synthetics. Keep it dry and air it daily. However, synthetics are useful if you cannot guarantee being able to keep your down bag dry at all times.
Sleeping sheet liner
A liner saves having to launder your whole bag. Cotton is quite adequate but silk is lighter and a real luxury.
Some people still use closed cell foam mats - those who have not tried Thermarests! But do carry a repair kit.
Unfortunately in remote regions most available fuel is usually of poor quality and high-tech stoves hate it. If you're going to rely on a stove, take one that you can easily strip down and clean, like the MSR XGK.
Calculate how much you need to carry between refuelling points. Make sure your fuel bottle is robust and made for the job!
Even if you have everything provided along the route, some 'nibbles' for the journey (or an emergency) are always handy. Dried fruit is nutritious and easy to transport. Depending on your style of trek and accommodation, you may need to carry a quantity of food for meals too.
Be prepared for extremes of temperature during a trek. In the lowlands it is likely to be swelteringly hot and humid, whilst above 5000m it can be dry, very windy and intensely cold.
Chose loose fitting shorts or trekking pants in light cotton or synthetic fabric. Women may find skirts more comfortable and convenient.
The technology involved in fabric manufacture has revolutionised the levels of comfort provided. Choose your high altitude wear according to the layering principle:
Next to the skin
Thermal underwear made of wicking material - takes sweat away from the surface of the skin before cool you. Patagonia's Capiline is superb.
Use a combination of fleece fabrics. Durable, light and quick-drying. In camp or when stationary, wear down jackets and trousers. Their function is to trap a layer of still air which acts as thermal insulation.
Windproof, waterproof, and (if the whole system is to function during aerobic activity) breathable.
Each element of the above system may be used individually, giving flexibility to meet various climatic conditions. Use the same basic principles to keep your extremities warm - gloves, hats and socks.
Personal medical kit
As well as any personal medication, it's worth having the basics to cover minor first aid needs with items such as sticking plasters, antiseptic cream, Compeed for blisters, antihistamine cream for insect bites, tubigrip bandages for knee and ankle sprains, plus Imodium and Dioralyte or similar rehydration powders for upset stomachs. In remote zones it may be necessary to take more specialist supplies for sterile equipment and water purification. There are a number of proprietary traveller's medical kits on the market.
Buy the best you can afford - with lenses that filter out 100% UV and IR radiation. Choose a design that fits your face closely or has removable leather side-flaps. Plastic lenses are light but scratch easily. Light levels are much greater at altitude and on snow.
Avoid sunstroke! Take a hat with a brim to protect your neck and ears as well as your eyes.
There is no such thing as a healthy tan, so take plenty and reapply it frequently.
Always useful for detached buttons, snagged clothing or whatever.
Super-glue is incredibly handy, along with a few patching materials and some adhesive duct tape, etc. For extended treks, you might consider carrying certain 'vulnerable' spares - or think about reinforcing what you set out with. Some items can be bought or repaired locally, so don't make your pack too heavy.
For keeping your stuff organised and dry in your kit bag or rucksack. Waterproof ones with drawstring tops are best but plastic bags will do at a pinch.
The range of Petzl torches are almost universal but do take spare batteries and bulbs. Keep it handy in your rucksack in case you get caught out after dark.
Must not leak! At least 1.5 litres, able to withstand boiling water. The Sigg range dominates the market.
Always handy - the 'Swiss Army' type is perfect though some now prefer the more industrial multi-tools based on the Leatherman range.
More usually used as a source of entertainment to measure your daily rate of ascent and descent but can be invaluable as an aneroid for keeping an eye on the weather.
Filters are heavy and expensive. A leak-proof bottle (with dropper) of iodine tincture is safer - add 2-5 drops per litre (depending on degree of contamination) and wait 15 minutes. Ascorbic acid (vitamin C) added afterwards neutralises the taste. Add any juice powder or rehydration salts after purifying the water. Bringing water to a rolling boil at any altitude will sterilise it.