Yeah yeah.. Leave it to the chick to help the poor guy out.
Ok, since it's outdoors, you want food that can handle not being in a deepfreeze.
Pitas and hummus
variety of cheeses (My husband is huge on the Brie and stilton... I'm not)
Grapes, fruit slices that can be hand fed... (Unless her family will be there.)
NO PINEAPPLE (don't ask)
A simple veggie plate from the grocer's, or make your own, with some dill dip. (Broccoli, cukes, cherry tomatoes, cauliflower) I prefer dill dip over ranch. Dunno about your girlfriend
If you want to "wow" her... Then make a few simple vegetarian dishes. My husband does these awesome grilled veggie hoagies, and he makes some killer veggie pizza. And yes, they travel well, if you're worried about them being in a picnic basket.