A great tip for keeping flies at bay, cut a lemon in half and add cloves to it. Set out in bowls about 30 min before food will be going on the table. The smell with leave your party pest free (at least the little kinds).
To keep flies away - Fill a zip lock bag with water and 5 or 6 pennies and hang it in the problem area - apparently, it keeps flies and wasps away. Some say that wasps and flies mistake the bag for some other insect nest and are threatened.
Keep flies AWAY from outdoor parties! Use lavender oil on a sponge & put it inside a can with a lid 24hrs prior the party. Open can & enjoy your food w/out flies flying all over your food. You could make a few and spread them along your food display. - rugged-life.com
how-to-keep-flies-away-at-picnics-Water and Penny Trick – It wouldn’t seem like putting water and a few pennies into a cup or baggie would help repel flies, but it does! This old trick from Latin America disorients flies and keeps them well away from you.