If you don't hike regularly or haven't hiked the AT before, I'd first go on a weeklong test hike. That'll give you an idea of what kind of gear you need or don't need.
The AT is a very well-defined trail that has fairly frequent road access points, so it's not like you'd be stuck out on a cliff ledge of some snow-capped mountain waiting for a rescue helicopter. Just be careful (
take off your pack!) when you pee off high ledges.
Knives:
I carry an AFCK on the trail. It's fairly heavy, but I trust the lock and I also EDC it back in civilization. The edge does get a little rusty after it gets soaked though, so I recommend dunking your knife in some kind of rust prevention treatment before heading out.
I don't recommend carrying a large fixed blade, because I really can't think of any purpose it might serve out on the AT. If you're making a fire for kicks, it can and should be made with a sparing amount of deadwood anyway, so you can just pick it up off the ground and snap it to length.
Multitools:
I brought a SOG Powerlock on my first week-long hike. That, along with overly safe water management, made the hike much harder than it could have been. On the next week-long hike, I took my Gerber Compact Scout multitool. Still too heavy (and not useful at all). Next time I'll be going with just a SOG Crossgrip or maybe a Micra.
Once I ran into two completely tired-out fellows sprawled out on a large rock on the AT. They told me that they were turning around to hike back to their car, because the trail was too much for them. I couldn't help but notice that one of them had a large folding saw clipped to the outside of their pack. They probably overpacked, and didn't have hiking poles to offload some of that weight.
Weight is a real killer.
