Still have much of the gear I used when I began backpacking seriously back in the 70s--Kelty external frame Tioga, Kelty Windfoil Breeze Tent, Peak 1 multi-fuel stove, one gallon aluminum pot...still works fine for me...surprisingly, it's not much heavier than "modern" gear...recently re-coated the backpack rain-cover I used on my thru and it worked flawlessly on a five-day rainy trip last winter...
If I hadn't checked out and devoured the two-volume set--Hiking the Appalachian Trail--from my college library I probably wouldn't have hiked the AT...a great read...taught me before I even hit the trail that just about any gear combination would work if you were enjoying yourself and had heart...still true today...
Even in '91, the year of my AT thru, much of the gear that I and fellow hikers carried is still sold by outfitters, or can be found on Ebay...
There was no internet when I planned my thru, so I sent away for gear catalogs and watched the mailbox like a hawk...
Echoing what's already been said a few times above:
There have been no "real" advances in rain-wear-- if it rains and you're sweating, you get wet...despite the "breath-ability" marketing...
Even in '91 I encountered hikers who I thought had the potential to give the rest of us a bad reputation if they went into towns and behaved naturally...some did ahead of me on a couple of occasions ...one can tell...
There were no "trail" angels seeking out hikers...but I met many, in towns, at stores, at camp sites...it all came naturally, and didn't feel "forced"...I was spontaneously invited into several homes for overnight stays along the way...I appreciated that...true local flavor experienced firsthand without the semi-commercial atmosphere of some of today's hostels...
My thru gear was "state-of-the-art" in the 90s...there's been little substantive change since then...synthetics have always dried faster than cotton, aluminum weighs less than brass, etc...
I didn't thru to "find myself", or to "party", I thru-ed because I loved the lifestyle...being accountable for only what was on my back, each day in a new spot, views, the unmatched delight at cold spring-water when you needed it most....
Wouldn't carry a cell phone if I attempted another thru...learned an everyday life lesson--if you don't carry a phone someone nearby will always be around to lend you one, if needed...translated: if you don't carry a phone the world is your secretary...
Sorry, no tales of flannel, jeans, or "waffle-stomper" boots....the more things change the more they remain the same....maybe...