I have had pedals causing creaking...it was on my son's MTB. Turns out the threads were partially stripped on the crank arm on that side. New pedals, new crank arm, no more creak.
Yes I suppose you could tie a messenger bag off to a rack if you wanted. I typically use a cinch type strap and a bungie for rack mounted stuff. Kind of a belt and suspenders approach. My son uses his messenger bag attached to him to save time. He can put what he needs in there for class, ride to class, lock the bike and go straight in without having to unload or unstrap a bag from the bike.
Aaron
