I also bring shelf-stable foods because the timelines raise food safety issues and trying to keep things "cool enough" is a challenge. Due to multiple food allergies there is little to nothing I can safely eat at airports or on airplanes [and I do not eat on airplanes unless medically necessary as a risk mitigation measure -- not eating on a plane means less chance of accidentally ingesting an allergen at 35,000 feet].
Snack bars, Wowbutter single serve cups*, two-packs of saltine crackers, Gogo Squeez apple sauce pouches* etc all travel relatively well and will tide one over for quite a while. *both subject to the 3-1-1 rule, unfortunately.
I am consisdering experimenting and making the equivalent of a wowbutter uncrustable sandwich -- freeze it overnight before the trip... I figure it should last pretty safely without refrigeration and will start out frozen so will actually be cool for a while anyway. Best part is it won't be subject to the 3-1-1 rule like the cups are

Not sure how the consistency will do though, am going to have to do some experimenting at home for lunches first.
SW