Decades ago I kept snacks in my car.

I never had much trouble with things. Candy would sometimes melt if it got real hot, but it was still edible.

It never lasted more then a few months anyway, so it got changed out before it had a chance to go stale.

Nutritionally there is not much difference between the average granola bar, a Cliff bar, or a Snickers bar, so grab a few extra bars of whatever you eat anyway and keep them in the car, and rotate them.

Granola bars (no chocolate) have an advantage in not melting if that bothers you.