For my PCT thru hike in 2002, my big purchases were a Feathered Friends Hummingbird sleeping bag, an Arc Teryx Khamsin pack, and a Marmot Home Alone tent (not recommended). I still regularly use the pack and bag, so spending money on quality gear that will outlast your trip is a good trade off. You really don't need much. Buy one pair of shoes (I used a mix of new balance trail runners, which lasted about 300 miles, and solomon trail runners, which lasted about 600 miles). You will have opportunities to buy replacement shoes along the way, and often your feet will spread a little resulting in a need for larger shoes. I used chlorine bleach for water treatment and esbit tablets for cooking.
The key to a successful PCT hike is to really move from the get go. You have a 5 month weather window and 2600+ miles to cover, 700 of it desert and high desert will 30 mile stretches without water in the beginning.

Good luck!

Bill