A buddy of mine and I did the Seattle To Portland (STP) bike ride recently, an organized event that takes place every year covering the 200 plus miles between the two cities. We did not have a chase car for support, so I needed a way to store my jacket, supplements, pump, food, tools, spare tubes, sunscreen etc. I've been using the Gossamer Gear Minimalistfor both training hikes and bikes so it was a natural to bring along. The simple design has no waist strap to contend with and the sternum strap keeps the pack hugging the back with no movement. I literally didn't notice it for 204 miles of riding. The simplicity of this pack means I grab it for any number of activities outside of hiking, and I've had no problems with durability in its second year of use. Weather was pristine for this ride but rain might have been a problem with the draw cord top, whose little hole will be an entrance point for moisture. Of course, the pack itself is not waterproof so were I to anticipate using this in the rain I would have to use a pack liner bag. The rear mesh pocket was perfect for attaching my number so I didn't have to pin it to my clothing. I saw lots of bike front packs and saddle bags during this event but I prefer to wear a backpack as long as the weight is light. This is a link to a blog from last year on the hiking/running aspect of use for this pack.
(caveat: I am a trail ambassador for Gossamer Gear and received this pack at a discount)