If you have problems eating outdoors because of yellowjacks here's a solution. Put a couple of sheets of Bounce around the table or picnic blanket and it absolutely keeps them away. I've heard it works on mosquitoes also, but since we don't have mosquitoes where we live, I don't know for sure. I do know about yellowjackets though.
Last summer, in Northern California, we had the worst year ever for yellowjackets. Some people swear by a few strips of bacon placed strategically away from, but near the food the humans are eating. Good luck. Consolation: this year isn't bad at all---yet. So, maybe you just have to deal with it for a few months.