Camelbak M.U.L.E. hydration pack with 100 oz of water, first aid kit, a couple energy bars, fire starter, goggles, and hat. Spot Messenger velcroed to the shoulder strap. H/t Greg Hilchey for that one.
Orlieb medium duffle. Capacity of 40 liters. Carries (left to right) Big Agnes Large Insulated AirCore sleeping pad, Kermit chair (I know--a complete indulgence!), 15-year-old Walrus Arch-Rival tent, and tent poles.
One of my 38-litre Metal Mule panniers filled with the packing peanuts that had been in the Great Basin, along with another maybe 8-litres still in the yellow bag, plus the (2) 2-litre bottle holders gives about a 50-litre capacity--just like Giant Loop says.