To know what to leave out and what to put in; just where and just how, ah, that is to have been educated in the knowledge of simplicity.
What To Pack
Using A Packing List
Arguably the single most important aspect of intelligent travelling is the issue of what to pack. This, more than anything else, will determine the size of your luggage, the weight of your load, and the state of your happiness. Your top priority, then, should be the acquisition, personalization, and use of a good packing list. "What to pack" is far too important to make up as you go along!
The world is awash with packing lists. Dozens have appeared on the Internet, and almost any travel store will happily supply you with what usually amounts to a list of the many things you might buy from them. And therein lies the fault of most lists: they enumerate the possibilities, rather than eliminate the liabilities. A list of stuff you might want to take is very different from a list of things you can't travel (comfortably) without. Even the venerable Universal Packing List is intended to be exhaustive, which rather misses the fundamental point (in the real world, of course, author Mats Henricson uses a much shorter list for his own actual travels).
Do I Really Need a Packing List?
Second, it helps ensure that nothing important will be forgotten. The go-light traveller in particular is only carrying items that are essential to the journey, so forgetting one of them can be especially inconvenient.
It's important to understand that you need a single packing list, not a new/different one for every trip. The purpose of a packing list is not to specify/record what you are taking with you on any particular journey, but rather to develop a model for your own travels, a constraint on your packing exuberance, a personal blueprint that you can refine over time (not change every time).
I've used the list on this site for more than a quarter century of travel around the world. I could probably reproduce it from memory. Still, I never fail to take the few seconds necessary to check it on every single trip. And, on more occasions than I like to admit, I've been reminded of items like a belt that I was forgetting to pack for the pair of trousers in my bag. It's no coincidence that aircraft pilots are required to complete a mandatory checklist — on each and every trip — before being allowed to fly the plane.
Don't pack list items that are unnecessary for a specific trip: parkas aren't needed in North Africa, nor are shorts in the Andes (for that matter, shorts are culturally inappropriate in many countries); malaria tablets & a mosquito net are unlikely to be helpful on a trip to San Francisco; dressy shoes might be dispensed with during an Amazon river trek; and you shouldn't need luggage locks when visiting your grandmother in Manchester (unless she has proclivities that might dictate otherwise). The list described in such detail on this site is intended to encompass items that are sometimes part of a one-bag traveller's needs, not always. It would be an unusual trip indeed that demanded everything on this list!
Add items if you must, to address your business needs, hobbies, personal requirements, etc., but resist the temptation to add non-essentials. If you're thinking "I might need this", you're likely mistaken; if it's "I can't survive without this", you may be right. But consider it carefully and dispassionately. Will the joys of listening to Radio America really warrant lugging that short-wave radio? Do you truly need that 200mm lens? Perhaps, though I have yet to hear of someone returning from an extended trip who vows to take more stuff the next time!