I've seen lots of commuters who ride with a backpack or courier bag on. When I start commuting I will need some way of carrying my usual assortment of stuff that I schlep back and forth to work, but I'm worried about slinging it all in my Crumpler bag because if I do come off chances are I'll land on it. I don't care about breaking my laptop, but I do care about my laptop breaking my back! (Even though I have a spine protector in my jacket...) So what is the general opinion of backpacks while riding? Should I be worried about it? Or am I worrying about nothing?