I think a bag with some fringe would be perfect with that outfit--very kicky yet still fits in with the casual look. Here's two ideas. Plus if you want something a little different, isn't this patchwork bag cute? Now for something totally off the wall, what about a sequinned purse. Provides a real contrast with tomboy look of the shorts and sneakers, but will definitely catch some glances.

Those fringe bags below will definitely look cool. Where I live I see lots of duffel bags +_o lol nike duffel bags come back in tons of colors and look sporty. I also think studded hold all bag will look cool.you can look at tons of studded bags on topshop's website. You can go on nike's website for the sporty look.

Really, any bag will go! All the ones Jackie posted are super cute! It really depends on you! If you like big bags or little, with the fringe, or not. You can always get a summer color, neon's or like a light pinkish tan... You can match it with the outfit!