Protect your food.
Store chilled foods in a cooler, and keep it out of the sun. Pack perishable food in one cooler and drinks in another. While you're en route, keep the coolers in the air-conditioned car, not in the hot trunk.

Drink up.
Bring lots of water and other drinks, but avoid dehydrating caffeinated or sugary ones. Freeze extra water bottles, and stick them in the food cooler -- they'll chill food and will be refreshing once they've melted.

Toss well.
Bring only as much food as you'll need. If you have leftovers, pack them in your cooler quickly. Throw away any food that's been left out longer than an hour.

Bring snacks.
Bring along nonperishable snacks, especially if you'll be active. Try nuts, trail mix, dried fruit and energy bars.

Pack the essentials.
Plastic tarp, for damp ground.
Paper towels.
Small cutting board (plus another just for any meat, fish or poultry you'll grill).
Picnic knife with a locking sheath (Messermeister picnic knife, $5; www.cookswares.com).
Ziplock bags for leftovers.
Antibacterial wipes.
Trash bags.
First-aid kit.