The butterfly lady, with whom I travel, is a truly brilliant packer. She can fit everything for a trip of any duration and variety into her backpack, no sweat.
I'm not one to be one-upped, so of course I carry everything in my pack, which is a less-adorned, yellow twin to hers.
All travelers aren't equal, though: She fits a much greater diversity of goods into her pack, and I think she winds up with more clothing options, too. On the other hand, I usually carry some oddball stuff (i.e. a spotting scope, or a field guide or two and binoculars in addition to a camera, etc.). Sometimes I volunteer for something heavy or bulky that we'll need & can share.
I do most of the same things she does, packing-wise: one pair of shoes, no full bottles, certain clothes as a cushion at the bottom of the bag. The biggest difference is I've taken a more radical stand on clothes.
For our most recent off-Homeland vacation, a three-week road trip in North Africa, I had two shirts, two pairs of pants, two pairs of boxers and two pairs of socks. I also brought a T-shirt and pajama bottoms. The trick was that I got all but the PJs in quick-dry specialty models (pretty easy on the wallet, which was nice) from a travel outfitter, and we were headed for a pretty dry place. Much easier on the laundry than Central America, I daresay.
As it turned out, I didn't like one of the shirts at all, so I only wore it twice in three weeks. The other shirt I kept clean by washing it nights and wearing it the next day even if it was still a little damp. In retrospect, I think I could easily have gotten away with one of each item instead of two, given the climate.
I couldn't speak for the butterfly lady, but as for me, packing lightly has gotten a lot easier since I:
a) bought those packpacks!
b) decided I'd carry only that pack while outbound (hey, some souvenirs are worth picking up an extra bag for) and then started a competition with myself to eliminate every non-essential item.
c) realized that you can almost always buy stuff on the road that is cooler than what you would have brought with you if you'd remembered it in the first place.
Of course, b) and c) have been the most fun, because I don't buy a new pack for every trip. But b) and c) really are fun, and because I value my portability, I don't mind buying new stuff every now and then to lighten that bag.
My moral for this story:
Unpack your mind before you pack your bag.