A real issue that I've whined about plenty in the past (and as recently as today to DW). Simply no easy and practical answer. These EDV (vehicle) bags in our case are really just GHBs. In my case, I don't *need* any food in mine, so it's essentially snackage that I rotate by consumption.

In DW's case... she's potentially got 30+ miles more-or-less cross country; not going into more detail on that other than to say Plan A for her is SiP at work until we pick her up. So it's an issue.

1. I came to the same conclusion as hikermor - canned hi-calorie stuff is best bang-for-the-buck.
2. A few TOTMs (We buy a new case each time we open a case) - these get rotated via lunchroom consumption 1 per month.
3. Water is a PITN in the wintertime. USUALLY it does not freeze solid very often stored in her trunk, but it can get that way; our vehicles live outside. Have a sensible plan (and try it out) to deal with that - which may wind up being empty or mostly empty containers.

YMMV...