For deserts, brownies are a big hit usually. If you can get a hold of some, vanilla ice cream with Hersheys chocolate syrup. Angel food cake. Root beer floats if you can find root beer. Another thing I've done is decorated strawberries. Dip a strawberry 2/3 of the way into melted white chocolate and then dip it 1/3 of the way into blue sprinkles, so they look like to colors of the flag.
I do a big BBQ every year with a few other American families. We have the usual burgers, hot dogs and chicken and various cold salads. One friend makes amazing baked beans and another one makes great devilled eggs, so they bring them every year.