I use a Kelty Antero which is just about the size of a regular school backpack but it has a lapbelt and side cinch belts for getting everything center (I have 22 miles RT). Its also what I go dayhiking with and it served as a diaper bag not too long ago. It has a large central pocket and an outside with little compartments for keys, phone etc. Its got a bladder pouch and place to fit a laptop I don't use. It also has a rain cover in a bottom pouch so its always there. If you deal with a lot of rain I'd stick with a cover. I've yet to see a real waterproof bag except those for river running. I fit my work clothes, all my food for the day, and my coffee in it (no shoes though). Thirty pounds sounds a little heavy for a commute. I can get get lost in the woods for three days with less than thirty. Where you off too?