Here are some of the resources I have found most useful for preparing to hike the Pacific Crest Trail. (Last updated April 2024)
Pacific Crest Trail Association – permits
Halfway Anywhere’s PCT page – tons of useful info, including surveys of PCT through-hikers
Plan Your Hike – especially their user-friendly list of resupply points
Far Out Guide – up-to-date trail information used extensively by thru-hikers. Cost is $40, as of April 2024.
Maps – Halfmile used to be the go-to site for maps, but as noted on the website, the Nat Geo maps are now the best to hand-carry. I used Nat Geo maps for sections that had detours, and I was very happy that I did.
PCT Water report – information about where there are reliable water sources, particularly important in the SoCal desert. I’m not sure whether these will be updated for 2024. The Far Out guide can be useful for water updates as well.
USDA’s Natural Resources Conservation Service SNOTEL reports – for tracking snowpack, which can affect water availability and trail conditions in the Sierra
Weatherbase – great for getting a feel for temperatures to expect on the trail. (For grins, check out how cold it gets in Idyllwild, near Mt. San Jacinto in the middle of the SoCal “desert” section.)
MacGyver's Travels 
T1D here, courtesy of another T1D who knows I’m curious to do the PTC. Will reference this from time to time. Thank you, in asvance, for providing this for the general public. Bravo!
I’m so glad it’s useful for you! I haven’t updated in a while, but these are still the pages I would rely on if I were doing it again. Guthook is now called Far Out. I’ll update that when I’m back in front of a computer. Best of luck to you! It is an incredible experience.