This bag is by Foley + Corinna Handbags and it's their Mid City Tote in River Stone ($444 at shopbop.com).
I love it for it's style and the fact that it's a convertible bag. You can wear it like you see in the photo to the right, as a tote. Or you can wear it as a shoulder bag, seen in the left photo here.
If the price is a little out of your range, you are in luck. I found two bags for under $25 at forever21.com...my go-to store for affordable trendy clothes and accessories
The second bag, seen below, is their Metal Ring Hobo ($23.80). It's a large bag, great for hanging out on the weekend.
foley+corinna handbag courtesy of shopbop.com
other bags courtesy of forever21.com