i have a big ol' heavy nasty backpack for my commute. it has to carry my lunch, my work clothes, my 1/2 gallon bottle of tea, the newspaper and whatever book i'm reading that day. it weighs more than the bike. it hurts my lower back. and my shoulders. and my upper back. but it's the price i pay to commute.

i tried a seat-post rack and i hated the change in the bike handling.

it's only 6 miles to work so i just bear it. at no other time will i put anything on my back, if i need extra water i take my camelbak fanny pak. for a ride longer than an hour i just cant stand any weight on my back. but for the commute and daily errands and minor grocery shopping it's way handy. the trips to the library are a challenge, books are heavy!!