During the summer there is an increase in food-borne illnesses for a couple of reasons.
One is that bacteria multiply faster in warmer temperatures. The other is because preparing food outside makes safe food handling more difficult.
Below are two sites that do a very good job explaining how to handle food preparation during the summer.
One thing the sites do not mention is to store your perishable groceries in a cooler with ice in it for the trip home from the store. Even a 20-minute trip home from the store in a hot car can potentially cause problems. Whole Foods provides complimentary bags of ice for that purpose.