+1

I'm actually using a dairy crate that a friend of mine found in the garage. I zip-tied to my rack and have more than enough room for backpack (change of clothes, laptop, wallet keys) and lunch. I could easily cram more stuff into if I needed. I use a carabiners to keep stuff from bouncing out, although the pack has a low center of gravity and would need a serious jostle (read: crash) to come out flying out of the crate.

I use a wedge pack under the seat to carry tools (extra tube, patch kit, pressure gauge, multitool).

If you already own a backpack that isn't water proof, just head to your local X-Mart and get a can of sealant that is safe for fabrics. You'll be all set. If you're extra concerned about keeping certain items protected (wallets, cell phones, mp3 players) you can put them in a large zip-lock bag, or purchase a water proof stuff sack from an outdoors store. I've used both methods to protect electronic devices and never had any trouble.


Hope this helps. Good luck!