Weight and space are the enemies of the long-term traveler. Whenever a friend hangs out and watches me pack my luggage after I've been in one place for a while, they're always amazed at how I sit and analyze whether to toss or keep any given piece of gear.
For instance, the USB-to-power-outlet adapter for the Amazon Kindle and the iPhone works for both of them. So, I threw one of them out. A friend was with me when I was packing, and he said, "Dude, why don't you keep both? It's tiny..."
And yes, it is tiny. But I'll probably make 80 decisions like that in a given year, and if I default to "yes" on all of them, that adds up to quite a lot. (Eventually, I threw out the USB-to-power adapter entirely, and I just charge both devices from phantom power on my laptop now)
This gets tricky, though, when you have something that's somewhat valuable but also bulky. When I got a new laptop, I now had two power cords/bricks. I've had a pretty nasty run of breaking power cords/bricks for whatever reason - just one of "those things," I guess - so I was sitting and figuring whether to pack both.
Eventually I tossed one.