Finger sandwiches, a meat/cheese tray, fruit tray, or some pizza. Maybe grill out.
One thing we always have at our parties (no matter what type) is a punch I was taught to make as a kid. You take Orange Sherbet and mix it in a punch bowl w/ Orange soda (or you can use lime sherbet w/ lemon lime soda). Its really yummy and goes over well esp w/ kids.