I appreciate the recent responses (Brad, Ross, Keith). I'm actually in China just now and somewhat jet lagged, so my response might not be entirely coherent, but just off the top of my head ...
I was surprised at the 18 ounce figure for "bags and sacks". The Ursack is a big chunk of that, at 7.5 oz plus another 1.2 oz for the odor proof liner. This might end up sent home; it's a balance between a little more weight vs. time and hassle spent each night in camp. Other than that, I count 5.3 oz, which all still does sum to 14 oz. I'm not sure where the other 4 oz are; I consider the 0.6 oz in bread bags as 'clothes'.
In fact, however, I found myself carrying extra ziplocks in a couple of sizes on the PCT last year, which even increases this. On the wetter AT, I'd expect to do the same.
Point taken, but when you say you only carry 3 or 4 bags, that's not much different from me --- one is the food bag. One is for clothes. One is for "small stuff I use a lot", and another is "small stuff I don't use so much" --- i.e., first aid kit, that sort of thing. I also have a ~waterproof bag that I carry my torso warmth layer in; I use the normal stuff sack for my sleeping bag and put that inside a plastic shopping bag from a store somewhere. Indeed it's a lot of weight in sacks, but ...
Bottles: I think this came up before (?) but the disposeable bottles I can adjust any time I'm at a grocery store --- or a garbage can, to lighten up. Pee bottle: even in 3-season travel, when it's raining much out or the bugs are bad, it can be quite nice to retreat inside a shelter and just stay there. Again, it's a disposeable container, easy to add or discard.
Electronics: yup, a luxury for me, and IMO worth carrying. The keyboard makes it much easier to write literally a daily journal entry, which I did on the PCT last year.
Cell phone can indeed play MP3's. It's a matter of (a) power budget, (b) DRM, and (c) storage space.
(a) With a light standalone MP3 player, I don't have to worry whether my music or audio book use is stealing power that I'll later regret spending.
(b) My phone isn't DRM compliant, which means I can't put audio books on it, and
(c) I couldn't anyway, as my particular phone only accepts a 2 GB microSD card, not big enough for maps and photos and various other stuff as well as MP3's and audio books.
Short answer: I think it's worth it. Maybe less on the even-more social trail that the AT is, who knows.
50 yards of dental floss: I've decided to use the original plastic packaging, and that's the key; dental floss itself is pretty light, and of course doubles as thread. Not worth focusing on, IMO.
Safety pins: yes, I've used them (drying clothes mostly), and only carry a couple.
Can opener (very light) --- in fact, I never did use this; I might on the AT, i.e., open a can bought in town and repackage contents. A pretty small concession to thru-hiking.
A second light: again, very small pinch type light. I used this once to change the batteries on my main light after dark.
Extra knife for spreading peanut butter: this is slightly handy given the low weight and discardability; I find the utility marginally outweighs the tiny weight penalty.
In fact I am carrying the pdf version of the companion, and that will be my only guide, other than printed data page style stuff culled from the companion.
"I hate the tiny screen" --- that's why I carry really small and light reading glasses.
Bushbuddy or the like: I'm not clear on when a wood burning stove is legal where campfires aren't allowed, and I would guess that on the so-populated AT that trying to get even twigs to burn on a regular basis might not be such a great idea. Alcohol is pretty easy to find.
Ibuprofin: maybe I will carry more, I had a lot more resupply boxes on the PCT ...
Again, thanks all for your feedback. None of the above is meant as "argument", but rather as "feedback on the feedback" !