In short: Yes!
Several years ago I started a project to try and backpack without synthetics. At the time I thought this was a bit of a "stretch goal". That is, I wasn't at all convinced it was possible, but I figured it would be cool to try.
At the time, was simply looking for a goal that would encourage me to do more experimentation. I considered re-creation, but while that's cool, it is antithetical to experimentation. I wanted to try and take old ideas and use them now, not just stick myself to what has been done. Anyway, I set out on a quest to see what could be done.
In particular, I wanted to see if I could build what I considered a "reasonable" though-hiker kit for doing the Applachian Trail. Having done most of that trail one summer, and spending my childhood vacations in the white mountains, I had a good idea what that might take. To define "reasonable" I decided to target a <20 lbs base weight, and around the same comfort and safety level as I had when I did my not-quite thru-hike in 2009 when I carried ~14 lbs base weight. I figured 4 lbs water 8 lbs food and you get ~32 lbs total... which isn't ultralight by any means, but it's lighter than many many thru-hikers do carry and would allow a good hiker to do a 3 or 4 month thru-hike.
When I told people about this goal, most people told me it couldn't done... not for a reasonable weight. I was skeptical that I'd ever find a reasonable sleep system that didn't weigh a ton. I wasn't sure about replacing my tarp either. Anyway... they were wrong and so was I. I'm still honing my kit, as all hikers always are, but listed further down is a kit that I'm convinced would work well and comfortably me on an AT thru-hike... for ~18.5 lbs base weight.
There is ONE piece of synthetic gear that so far I'm unwilling to replace, and that is my shoe soles. Rubber is just too good for shoe soles. Recently when I was learning a new technique for making my own shoes (the result of which are my primary shoes right now), someone with a LOT of experience in the matter told me that leather soles only last ~300 miles. I'm sure you can extend that by making them extremely thick and stiff, but then the grip is bad, which can be downright dangerous. Also, it ruins the natural human gait. So, for me, this is the one place I will not give.
Note that I'm really not cheating here. This list is missing the drugs for my medical conditions, and that's it. There's no underwear because I don't wear it. Stuff that is sometimes worn and sometimes not is listed as part of base weight. I've tested this gear in torrential downpours, and below 20F. Some of it might want minor robustness tweaks I'd do before taking it on a full hike (my sleepingbag could use a reinforcing triangle of buckskin where the ties join the leather), but it works for me.
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For any gear that isn't blatantly obvious, you can almost certainly fill in the search box on the right of my blog and find out where I got it or how I made it.
I actually think I can cut even more weight off this. The blanket pack I'm experimenting now should cut another ~1.5 lbs, bringing my base weight down to ~17 lbs.
The ultimate test would be to actually DO a thru-hike with this gear. Angie and I had actually intended to do a PCT thru-hike, before we realized that the west coast is almost continuously on fire these days. It would be miserable with all the smoke, and quite possibly deadly for me with my asthma. That leaves an AT thru-hike... which maybe we'll do eventually, but just isn't nearly as motivating for me having already hiked a huge section of it. A PCT thru-hike would of course require a few tweaks. Warmer boots, like the ones I recently learned how to make, a way to carry more water, and maybe an alpenstock like the one I've already made and partially tested... but not a lot more than that.
So, after all this experimentation, what was the hardest piece of gear to drop besides shoe soles? Answer: Gaskets. Most of this gear works so well that I have no intention of ever going back. I love my cotton tarp, my waxed jacket, my canvas shorts, my wool sweaters, etc. But... gaskets are hard. For smaller mouthed waterbottles leather works well enough, and I'm going to keep using it since it works fine. But, for my BOT, (which I love, since it cuts out an entire cookpot from my gear), I couldn't get the leather to quite seal like I want. silicon gaskets are amazing.
Obviously what I'm doing requires more knowledge and skill than buying the standard gear set at REI does... but, personally, I find it more fun and fulfilling. If nothing else, I hope that others look at my experiments and realize just how little gear you actually need... and how much less than that you need to purchase.
Go out, have fun, and HYOH!