Wow!! Where to begin......

If you really are contemplating a scenario that could involve a 400 mile trek, you should really get some experience with that pack. I suspect that there are many models more suitable for your purpose than what you have. What is its capacity?

Weight will be a big issue for your trekking scenario, and yet, relatively trivial if you can drive all or nearly all of the way. MREs are way too heavy for continued. backpacking use - many more favorable foods are available; many can be found in typical supermarkets. At the same time, you are not carrying enough water - that pipsqueak stainless steel canteen should be replaced by something with more capacity, unless your route takes you along a nice river.

For that matter, what sort of climate, terrain, etc. are involved in your planning? That makes a huge difference, to say nothing of seasonal changes....

If I were planning an emergency trip of this nature, I would seriously consider utilizing a good touring bicycle, which will compress a twenty-five day trip (at least) into a more negotiable 5-6 day trip, provided you have the conditioning and stamina for either mode of travel.

Are you sure you have no safe havens any closer than 400 miles? You will need at least a few places where you can rest and regroup for at least a day or two.

Good thinking, and thank you for an interesting problem. This should be a lively thread.......