I third Banjo Brothers. I have the white version, medium. I like how it has no internal compartments so you can custom pack every load and how the roll top allows you to essentially customize the size of the bag (read: want to make an impromptu stop for groceries and a six pack on the way home? Not a problem!). I used it through the hideous Philly summer and found it reasonably cool for a backpack, and it's truly waterproof. I also get lots of compliments on it, which always makes a day nicer.