I love... LOVE my half pint Jansport bags. I own about 5 of them and take them everywhere from parks, to fairs, to parades.
They're small enough not to be considered a real backpack - more a purse, and large enough to carry two bottles of water, a wallet, and a thin shirt/ sweatshirt comfortably.
http://www.jansport.com/shop/en/jansport-us/half-pint-tdh6
They have all sorts of fun designs and it's a Jansport brand. Jansport has a lifetime warranty on all bags. If they're damaged they will either fix the damage (Re-zippering, re-sewn bottom, etc.) for simply the cost of shipping it back to them or they'll replace it and send you back a brand new bag.
I had a really old Jansport leather bottom bag I bought at a goodwill I'd had for ten years. I LOVED this bag. But the bottom ripped out and the straps were fraying. I sent it back to them ($5 or less shipping) with a note that I didn't want a new one, because this was my FAVORITE bag and could they please fix it? And they sewed in a panel and fixed the straps and sent it back to me for free.
I back Jansport 100% - not everyone knows about the warranty though so I feel like it's an underutilized brand.