Pannier 1: 2 liter water bottles, lunch container, untensils, books, writing tablet
Pannier 2: Pants, shirt, underwear, sock, belt, towel
Outside Pocket 1: tire change kit, Allen wrench, lock and chain
Outside Pocket 2: wallet, cell, keys, pens
Messenger Bag: Laptop
I subtract what isn't necessary, and have room to stash stuff I might acquire during the day.