I use the Ortlieb Back Roller on the back. The front low rider position has REI panniers hanging from it.
I use the rear for water proof needs and the front has some pockets.
BTW - Nylon bags of various size and colors really help organizing for me. I also have a cheat sheet that I keep in my front handle bar bag, (BTW, waterproof Ortlieb.) The cheat sheet has all items that you will find in a particular nylon bag & pannier. For me it works great if I always return items to the same nylon bag and stuff that into the correct pannier.