Go for the happy hour -- $5 glasses of good wine on a lovely patio are always the best way to spend an afternoon! The wine selection here is always excellent, especially the whites -- I'm normally a red wine drinker but at Postino I feel confident branching out to the pale side.
As for food, I've never tried a bruschetta here I didn't like, it lives up to its reputation. I also recommend the brunch on weekends: the menu is somewhat small but the choices are delicious -- I've had the farm scramble and also the walnut bread with brie and jam is to-die-for.
This being an Italian sort of menu, there isn't much in the way of gluten-free options, but if all you can have is wine, there's nothing wrong with that!