Barb is awesome about this stuff!
Fruit is a great portable snack. I love popable veggies like carrot sticks and grape tomatoes. Like Barb said, invest in a small cooler and keep it in the car.
Soy nuts are good, as are other nuts (just keep to a serving!)
Cheese sticks are very portable and easy to grab.
Natural pB is even better in the heat (easier to spread!) and you can bring Triscuits or other SBD safe crackers (pita, WW mini bagel, etc.) to spread it on.
It's awesome that you're planning ahead, hon!