I am in my car A LOT for my job as we drive to client sites across 3 states.

As previously stated it can be difficult to find foodstuffs that can withstand the temp swings (110+ to -20) of the seasons in MO/KS.

Currently what I am using is granola bars (the hard crunchy kind). They are prepackaged, can be thrown into a pack easily, and hold up to temps very well. I eat them for "lunch" often enough on the road that they get rotated pretty often, but even if they didn't I think they would be viable for quite a long stretch.

As a friend of mine stated, they are the modern day equivalent of hardtack only they taste better.

YMMV,

Greg