I guess you could also call this post "PCT gear review."
Note: UL means ultralight. There is a trend among backpackers to carry gear as light as possible.
Note II: Always look for gear at a discount. Steep and Cheap is my favorite, but you get almost any piece of gear for a discount. Just because someone has a pack full of nice new gear doesn't mean they shelled out for it.
Note III: There is almost never an end all, be all for any single piece of gear. See what fits for your style and budget. These are simply my observations and opinions.
As someone who had never really hiked before, it's a nice primer for the PCT and lightweight hiking. The 'book' section of the guide helps you figure out if this trail is really for you. The 'trail guide' section is a nice supplement to Halfmile while you're actually hiking. It's by no means necessary, but I don't regret buying it. Remember to hike your own hike (HYOH) and not simply follow Yogi though.
I personally didn't use Halfmile maps, but they are great if you are a visual person who likes to see topo maps. The elevation profiles at the end of each section are the best. They're free to download, but you still have to print them.
Indispensable. This was the No. 1 way for me to get trail data. You get distances and up/down to pretty much anything on trail, especially towns and water. It doesn't do everything, but the features it does have work very well. Free. Available for iPhone and Android.
At $6 per section ($30 total), I found the Guthook apps a useful and worthwhile companion to Halfmile's app. I did most of my navigation via iPhone, and Guthook was helpful as a map and for finding campsite locations. Available for iPhone and Android.
Smart Water bottle and wide mouthed Gatorade bottle.
Smart Water bottles are great because they use space well on the side pockets of your pack since they are tall and slender. They are less fussy to get in and out while you're walking too. Having one wide-mouthed bottle was handy for putting in drink mixes like Crystal Light or Nuun tablets. Each of these are lighter than your heavy duty bottles like a Nalgene. You will get laughed at if you carry a Nalgene. They're so heavy.
Platypus / SoftBottle 1L (1.4 oz)
During the desert you may need to carry five liters of water at any given time. During certain sections, you may even need to cary six (coming out of Tehachapi, Hat Creek Rim and leaving Crater Lake). It's nice to have an extra liter or two of storage that is compressible when you're not using it. This is a great choice and pretty much everybody uses them.
You mix seven drops from two different bottles, wait five minutes, put it in your water and then wait another 20 minutes. I loved these for the desert where we would get three to five liters at a time, but found them a bit more tedious for the rest of the trail where you only need to get between one and three liters at a time. I didn't notice much of a taste either.
Sawyer / Squeeze (3oz)
The plus side of the Sawyer is that it fits on a SmartWater bottle. You can fill up your bottle and drink straight from the bottle with the Sawyer on it, if that's your thing. Also, it filters out debris that you might have picked up your water. Otherwise, I found the Sawyer to be slow and inconvenient. I didn't use it much and we ended up sending it home.
Regular, unscented bleach. Two drops per liter. Wait half an hour and you're good to go. I switched to bleach somewhere in NorCal and never regretted it. Just don't add too many drops or it'll taste terrible and can destroy your stomach lining.