Good place to shop for a neat backpack or day bag in the Bay Area?

I’m looking for a good sturdy everyday bag that’s got to carry a lot of folders, books, and oddly-shaped items – but ideally looks at least somewhat interesting and maybe even “adult” (as a graduate student/professor I’d rather not use a school-kid backpack anymore!), or at least isn’t covered in a bunch of plastic and straps (hopefully you know what I’m talking about). Where should I look for this?

Thrift stores, markets, regular stores, sports stores, etc. Places that seem obvious to you, places one might not think of.