Maybe this should be a survey - what kind of bag does everyone use - is best for running erands - commuting? Do you use the same bag, more than one bag? For commuting I have a messenger bag or backpack - for work I will just need to carry tubes, tools, lock, lunch, raingear, pda, zune. But for running an errand(no more than a bag of groceries) is a rear trunk bag or pannier best? I think the pannier might be too big and pricey.
Thanks