Every guidebook and packing site has a different packing list (and we include one here). However, it really is a matter of personal preference and each person has different requirements and tastes. The one over-riding rule is to Pack Light - in all cases it is better to bring less, not more! What you pack, what you bring it in and how you pack it can be a major travel decision.
"Even the elephant carries but a small trunk on his journeys" - Henry David Thoreau
In most countries you can buy almost everything you could possibly need for travel, so it is much easier to pick up additional things you need while traveling than to throw away stuff that you don't need. Traveling light is a HUGE advantage giving you flexability, ease of travel and many other advantages.
Choosing your luggage is an important decision, it determines how easy it is for you to travel and how much stuff you can take. You will want to choose it based on transportability, security, durability and accessibliity. Backpacks are still the most practical way of carrying around your gear on a long trip. For any travel you will also want bring along a day pack.
Choose clothing that will allow a minimum amount of items to be carried. This is done by selecting items that can be mixed and matched together, based on colors or styles, to create a variety of outfits. Choose the basic essentials that you will need but ensure that they are versatile enough to be easily combined. Try to choose functional clothing items that will offer protection from the elements yet will be comfortable and easy to care for. You need low-maintenance clothing that will be flexible enough to keep you warm and dry, if need be, yet also be compact and light enough to carry in your pack.
This list is designed to be a general guide and is not intended for a particular country. Obviously, this list would be altered depending on your destination, time of year you're traveling in, importance of comfort, amount of money you will have and length of time you will be away. Each traveler will have their own priorities and will thus develop their own list, but this is a start.
It is always wise to pack a small medical kit with certain essentials that may be required during your trip. All medical supplies can be taken in a small case. It is probably a good idea if this is at least partly waterproof and made of a sturdy material so your medications don't get crushed. It is generally not necessary to take a large first-aid kit as you mostly need it to handle emergencies and have on-hand a few commonly used medicines that will hold you over until you can resupply.
Pack Light! In these modern times of the global economy you can buy almost everything anywhere - what that means is that you can pack light and still survive. Ask most extended travelers and they will tell you "Less is Better". You do not need to pack a years supply of essentials. Traveling light is a HUGE advantage and it can be done. The old motto is "Lay out everything you are planning to take only half of that".
Of all the pieces of clothing you will wear, what you decide to put on your feet is one of the most important decisions you will make. Choose your footwear carefully as you will be spending plenty of time walking, whether you plan to or not. Your choices of shoes will most likely depend on what part of the world you are traveling in (particularly weather and terrain) and what activities you intend to partake in.