I'm sure this is going to sound totally unappreciative but if you're going to give a gift, make sure it's small token of appreciation, like "put it in your purse" small. It's a P.I.A. to carry around something like a bouquet of flowers for the whole date.
Try something like two fancy chocolates in a box. Y'know like they do at Godiva and the nicer chocolate shops. Or gourmet cookies and always give 2.
One for her and one for sharing ;)