My wife's allergic so we are always extra careful.
We hang a fake wasps nest from the awning as we are setting up and then put out a few homemade traps.
The traps are simple to make, just take a plastic pop bottle and cut the top off just before it starts to get smaller in size (cut piece will look like a funnel). Invert this and either staple or tape it into the bottom of the bottle. Add a bit of apple or orange juice and either hang it up or put it somewhere away from where you eat. The wasps get in and can't get out.
And as so many others have said, never leave a drink un attended or open.