I almost forgot electronics!
Just as an intro, I want to mention that I tried using a paper & pen journal on an earlier backpacking trip. I wasn't satisfied with a paper repository, so when I got back, I typed it into the computer anywhere. Photos without a journal (earlier trips) weren't enough; I tended to forget what happened or the details of the photos. So this time I did the electronic blog...
I carried an AT&T iPhone 5s (in a waterproof Lifeproof case), a Ricoh WG-4 waterproof camera with an Eyefi memory card, a Verizon MiFi with 4,000 mAh backup support for other devices, and a Sansa Clip Sport for music and audio books. I also carried a wall charger, a car charger (for GPS in rental cars), and three cables. I also had a backup camera battery and memory cards.
When I started the AT, I also had a 12,000 mAh backup battery. But I sent it home from Hiawassee, GA. I wasn't using it and it was too heavy.
I transferred photos from my camera to my phone each night using the Eyefi (via a WiFi signal). I wrote the blog in BlogTouch Pro on the iPhone. But I found out that without lots of bars of signal, the uploads failed with full sized photos imbedded. So I used a Reduce app to convert the photos I wanted to post to around 640x480 pixels. I still needed a moderately good signal to do blog uploads, but it didn't have to be high strength. After reaching a good computer, I substituted full sized photos for the low res versions.
I also embedded a screen capture of the elevation profile from Guthook's AT Hiker app into each day's blog.
Typing on the iPhone's virtual keyboard was slow, so I took 30-45 minutes to write each short blog. I found that BlogTouch Pro occasionally lost a blog saved to local storage (awaiting upload). So I tried using Pages as the initial app to create a blog's text, but found it was buggy, especially with copying and pasting out of the app. My last solution was to create blog text initially in Word, then copy and paste it to BlogTouch Pro. Word has a nice interface and seems very safe and stable.
During the day, I kept the iPhone in airplane mode (no cell radio function) and the screen off. It usually lasted about 5 days this way. I used the WiFi only to transfer photos. I would get it out occasionally to check my GPS location in the AT Hiker app. But I found the AWOL Guide pages I was carrying to be sufficient for locating my position most of the time. I also checked for signal on some peaks, and when it was present downloaded and sent email. I never had to recharge except at town stays, but it was close a couple of times.
The Ricoh camera seemed to use a lot of power when I turned on the Eyefi WiFi function. I would guess it probably would last 4-5 days with my approach to use. I turned it on for quick photos, and then quickly turned it off each time. It never fully drained, but I would still keep the small extra battery.
The Eyefi card itself never came close to being full. But I did carry a non-WiFi SDHC card in case the Eyefi failed. The Eyefi app on the iPhone supports uploading all photos to an Eyefi cloud, but I found that required a lot of signal or a strong WiFi access point.
Other hikers seemed to get text message capability via Verizon when I was seeing no AT&T service. But my Verizon MiFi was usually buried in the pack (it's not too light). I don't have text on my AT&T plan anyway, but that poor a signal wouldn't have supported a blog upload anyway.
If I did it again, I would probably leave the Verizon MiFi at home. I only used it in Hiawassee and Franklin. That might allow me to carry a slightly larger phone like the iPhone 6 or 6+ with an easier keyboard to use.