Liza, how tall are you? Right now I use a Camelbak with the bladder taken out, but it is a woman's model because I am really short (5' 1"). Also, I can't really get a lot of stuff in there. I commute on my road bike because it's light and fast, but I can't put a rack or any kind of bag on it because my seatpost is so low and the carbon, etc. I like the features of the pack you describe, esp. the hip strap. I tried riding with a regular (kid's sized) backpack, but it killed my back. The messenger bag I tried was waaay too big for me and I felt really unbalanced.