Basil will keep flies away (I sprinkle fresh bruised basil around our picnic areas as well as grow them near the patio); yarrow will keep some insects off the skin (I have them growing in various places in the garden so it's easy to pick a bit and rub it on bare skin); and there are more 'natural' repellents. I'm not sure about wasps and yellow jackets. It's the mosquitos that I try to avoid.