What an adventure lies ahead of you!
You already have some suggestions for dense, compact food. I’m thinking beans, lentils, oatmeal, rice, bulgur, barley, biscuit mix and cornmeal all pack well. Being dry, they can handle the hot/cold conditions that being in your trunk may subject them to. (Not as much the biscuit mix (shortening) and the cornmeal.) Do some reading about combining foods to get all the amino acids you need for complete proteins. Beans and rice are a classic combination, as are beans and corn. The aforementioned dry foods probably will be OK without vacuum packaging.
Dry milk will deteriorate if exposed to air, humidity, and probably prolonged heat, so you may want to carry a smaller amount and maybe buy Nido in cans or quart-packaged rather than bulk-packaged powdered non-fat milk.
Look around a bit and you should find some dehydrated veggies to add to your meals. Tomato sauce can be dehydrated or you can buy tomato powder. The same goes for bell peppers and parsley. These are the dried vegetables that I’ve found easiest to locate, and they are fairly versatile. I believe that, like milk, they will be more sensitive to humidity and heat. If you have a dehydrator, you can dry your own vegetables. If you also have a vacuum sealer, you can make your food last even longer. Pack enough for a few days or maybe a week, then vacuum seal. I like to clean and reuse mylar snack bags, such as snacks are packaged in. I used to collect them at school, but no longer. Larger chip bags can be cut down and sealed into smaller bags with a clothes iron. Suck out as much air as possible with a straw before sealing. These bags will stand up to boiling water, should you wish to use these for your backcountry foods.
I rather liked the idea of picking up local fresh veggies from farmer’s markets, etc. Pick up some eggs and cheese, and maybe small amounts of crackers, meats, nuts, and nut butter along the way, too. Don’t forget your favorite basic spices, sweeteners, and salt. Cinnamon does a lot for oatmeal, and can work in rice, bulgur, and barley, and cornmeal mush the same way. I can’t imagine rice and beans without spices. Look up a bunch of recipes from different parts of the world to give yourself some variety.
Good luck and have a blast!
CamperMom