The short answer, more than you might think. The long answer? Shorts, chamois, jersey, socks, gloves, hammock with straps, first aid kit, granola bars, Cliff Blocks, lighter, multi-tool, hand/CO2 pump, tube, shock pump, knife, headlamp, keys, and a wallet. And that's just inside of the pack. The Lid Lock does a great job holding your half shell and my SixSixOne knee pads strap onto the side of the bag very easily. All this means that this pack is big enough to do an overnight trip if you really wanted to.
Carrying a lot of stuff isn't useful though if you don't like riding with the pack on. So with all this stuff still there, I threw the bag on and hit the trails at FATS (see last post). Once I had the straps set how I wanted, the bag was extremely comfortable. It sits well and never moves. I was really impressed with how stable it feels, even loaded down. It has yet to rub me in any funny way or make me feel constricted. Even on my first ride with it loaded down, I put in around 40 miles and not once was upset that I had it on. It also is extremely breathable. There is a mesh back with cut outs to help airflow and keep you cooler. Even on days with a heat index well over 100 degrees, I felt just fine.
The Osprey pack has great durability so far as well. It has seen a couple hundred miles of riding, a few falls, 115 degrees, heavy rain, and the Chomolungma Challenge (30,000 feet of descending!). No strap has moved, or started to fray, or anything along those lines. Buckles all engage still, the bite valve still works flawlessly, and the Lid Lock system still holds your helmet securely to the outside of the pack. And to make it better, this pack full of awesomeness is backed up by Osprey's All Mighty Gurantee. What they say is that any reason, any product, any era. If it breaks, they fix it.
"Osprey will repair for any reason, free of charge, any damage or defect in our product – whether it was purchased in 1974 or yesterday." - ospreypacks.com
Overall, I like this pack a lot. A whole lot. I would recommend it to anyone. Whether you are doing XC rides or going on two day bike camp trips, and everything in between. And if you need even more storage and space, they also make a Viper 13. And if THAT isn't enough, they make all the way up to a 36 liter pack with the Manta line up. All of which are available with 1.5-3 liter Hydraulics Reservoir.
So load up your pack and grab your bike! It's time to ride all this way!
