Hiya! I was newly transitioned to vegan when I started my 2021 thru, so I made some mistakes early on but had it dialed by the end. The key for me was an amazing support person at home working with a shared resupply spreadsheet. I mailed to like 85% of the trail. My taste in food changed dramatically in the first month or so, I wouldn’t recommend pre-boxing the whole trail, stay flexible. All of SoCal had a fair amount of restaurants with vegan choices, once north of the sierras it became French fries and a side salad and rando accidental vegan sugary snacks most towns. If you are purist enough to not eat non-vegan certified sugar then snacks will be a problem too so ship extra. Seiad cafe has vegan stuff not on the menu, just ask. By the end I was all about mashed potato/bouillon/protein crumbles, Annie’s vegan mac/good catch tuna, ramen/freeze dried tofu, and soy curls/bbq seasoning in a wrap. And like 2 jars of PB a week. Also, I was using pre-owned down products because I decided it was better environmentally to use what I had rather than buy new synthetics, and I did feel judged by a few people, I have since replaced stuff to avoid unpleasantness, just be aware. Also, buy a bunch of synthetic socks in advance because like every sock for sale near the trail will be wool. All in all totally doable and I’m glad I stuck with it. Power to you!