You could easily fit a week's worth of underwear, socks, a pair of jeans and a shirt or two in it plus a laptop and ipad depending on how much other stuff you were trying to carry.
They carry them at target last I checked if you wanted to take a look - the bag kind of expands like an accordion when start putting things in it. It has 3 zipper sections - a large compartment, a medium, and a smaller half sized one on the back. The medium one fits my laptop, ipad, and an accordian file for receipts and other paperwork, 60% of the bag is still empty for other crap after that.