Q1. How many clothes should I bring, and what sorts?

A. The minimum possible naturally! However, they must be "dual-use" wherever possible, as you may have to get into places looking at least vaguely smart. It's also a good idea to get things that dry quickly after washing. The following list is a suggestion:-
-two pairs of "hiking trousers" which can look smart when necessary.
-two long-sleeved shirts that can also look smart with the trousers.
-three T shirts; need I say more.
-three sets of underwear and hiking-type socks (you won't use any more!).
-thermal underwear if you are going somewhere cold.
-jumper/fleece.
-a warm and smart jacket which is water resistant (difficult but possible).
-balaclava.

Q2. What about boots?

A. Very important; you will find it hard to get decent ones abroad. They should be suitable for hiking but not too heavy as you'll have to wear them all the time or near enough. If you want to exercise or just for comforts sake, it's a good idea to get Sorborthane insoles too. They should be smartish and able to fit with the trousers/shirt, and I'd advise against getting waterproof ones! Wear them (and your feet) in before you go.

Q3. What about a rucksack?

A. THE most important question! There are several important requirements.
-capacity; get something too big rather than too small, though about 70-80l should be enough.
-do not get a rucksack with a zip on-able rucksack on the back; they don't work when hiking as they drag your shoulders back. If you want a zip on solution get one with side pouches that can combine to form a single day sack.
-the choice between zip-open rucksacks and the top fill type is still open; they both have advantages. The former allows easy access and the ability to packlock against casual theft, the latter is more robust and waterproof. Your choice!
-it must be comfortable to carry for long distances; a proper hip belt etc.

Q4. What about sundries?

A. I'll assume you all want to wash yourselves and you know how hard it can be to get things like toothpaste at times. Another useful bit to carry would be a clothes line, plus washing fluid.

Q5. Anything else?

A. If you are to do any hiking in Tibet a sleeping bag and tent/bivi bag are obviously essential; bring a compression spider for the former. A large flexible water bottle is good for hiking too; I used a 4l one. Some good sunglasses will stop you from going blind; literally! Finally, a pair of flip-flops are fantantastic for preventing foot infections, so take some or spend half the trip rubbing in athlete's foot cream- I did.
Back to frames- if you're not in them already!