Before the trip:
1) Freeze couple of slices of homemade cold pizza, crustless quiche, omelet or frittata
2) Make a lentil/bean salad
3) Pack a couple of sandwiches. I do one that's sweet, like PBJ, and one non-sweet, like hummus, sun-dried tomatoes, mint, cucumber, olive tapenade.
4) Make a protein shake. I use bananas, berries, avocado, nut butters or silken tofu, spinach, flax/chia seeds etc.
5) Make or buy some fruit leather.
6) Cook a big meal - rice and beans or tofu stir fry.
7) Pack some trail mix/nuts, chickpeas roasted with salt and lime juice, baby carrots, frozen grapes, apples, bananas etc.
For a 14 hours back-to-back, with your flight schedule, this is what I'd do (been on 20 hour trips):
First meal: Eat a protein rich meal before you head out for the trip (I eat a big meal like rice and beans, tofu stir fry, etc.). Carry a protein-shake on your way to the airport and sip along (finish before you enter security). Rinse the container for refilling with water later once you cross security.
Snack: 2-3 hours after meal #1, i.e., after your first flight, at the intermediate flight, before boarding the second flight. PBJ sandwich, lentil/bean salad, baby carrots, apples, etc. for a snack. Drink lots of water.
Second snack: As soon as your second flight takes off, have a sandwich. Have a non-caffeinated beverage (e.g., water, juice). There will typically be kids who cry during takeoff/landing, so you can't doze off right away anyway.
Nap for a while. Say take a 3 hour nap. You are going to need it. Wake up before your flight lands.
Meal: Have the couple of slices of homemade cold pizza, crustless quiche, omelet or frittata (thawed by now). Lots of water. Do this right after you get down from your second flight.
Third Snack: Fruit leather, trail mix, apples, oatmeal/protein bars etc. Right before boarding your third flight.
Eat up any leftovers before your hour long drive to destination. I don't know your calorie needs or metabolism so adjust portions accordingly. In general, eat perishable stuff during the earlier portions of journey.
Don't hate yourself too much if you did have to buy one meal or a snack at the airport. Drink lots of water. My rule of thumb is at least two cups of water every hour. Adjust accordingly depending on your hydration needs.