We've had the same kind of party several years in a row. In fact, we usually have two birthday parties for DD - one for our family and "adult" friends and one for her schoolmates.
Since there are more kids at the "school" party, we keep the menu a bit more kid friendly. Chips, fruit, hot dogs/burgers/lunch meat & cheese tray, veggies, cookies, cake and ice cream, lemonade and iced tea (since parents are welcome to stay we also serve beer). We serve all the food in the kitchen (which is right off the backdoor) to keep flies and pests to a minimum.
For the adult parties we usually get a little more extravagant with the main dish... but the last couple of times we've just gotten take out brisket from a great BBQ place in town. We've done our own BBQ chicken, turkey and ribs before, with potato salad, baked beans, a big mixed green salad, etc... Chips and guac or seven layer dip are always a hit. We usually serve sodas, lemonade, iced tea, beer and wine at these parties.