As a general rule, unless it is otherwise specified, wear a conservative dark colored suit and tie. No funny colors... black, blue, really dark grey- they all will work, but you want to present a professional and conservative look.

If they specify business casual, I'd personally wear nice slacks and a button down collared shirt without a tie, but possibly a sport coat, depending on the corporate culture at the company (if you know it).

As for the briefcase/backpack/whatever, I've always been fond of keeping it simple and low key. I take a notebook sized (9"x12") executive leather portfolio with a notepad, a nice pen, and several copies of my resume/supporting documents inside. My logbook is an electronic printout that is also in a leather bound 3 ring binder. That's all I carry into the building. Leave everything else in the car (including your phone!).

Good luck!