A couple of thoughts on TWP's and RR's choices:
1) Soy beans: I refuse to eat any soy product if I know it is an ingredient and can choose almost anything else. Soybeans are one of the reasons that the health of Americans is on the downslide. I will not ask anyone to believe it, nor am I preaching it, but I will ask anyone that is interested to do some due diligence research on the generally not mentioned negative effects that soybeans and soy products have on the human body.
2) Squash/pumpkin: I would only grow a squash if I really needed to do Three Sisters planting. While I like pumpkin pie, I much prefer carrot pie, so have no need for the pumpkin squashes. The only squash I really like is yellow crook neck summer squash and that is just not a good choice for a prepper basic garden.
3) Beans: While I like pinto beans, especially cooked with a hambone, I would not make them a first choice. Nor kidney beans. For the same basic reasons. Both can become very difficult to cook to a consistency that most people will accept after long storage. And the very fact that makes them a top choice for many, is the stronger taste they have. It can be a bit much for me in anything except 'a pot of beans' type dish. For other purposes, as an additive or stretcher for other dishes, I think they affect the taste to a degree that keeps many of the dishes from being what they were intended to taste like, and turn them into a bean tasting dish.
4) Corn: I find that quality field corn, for those few hours when it is in the milk stage, is superior to all but the highly modified Super Sweet Corn strain of sweet table corn. But if you do not harvest and cook or preserve the field corn during that short window of time, field corns in general are not great table corns.
Now that I have voiced my thoughts on other people's choices, I will voice my own choices for a basic seven. (Which, truth be told, I think is a highly arbitrary number that does not represent a well rounded prepper basic garden grown from stored seeds.) (I am hearing something in the background here... 'Who are you to make judgements...' Hm... need to clean out my ears, I guess.)
All heirloom open pollinated varieties suitable for the area soil(s) and climate:
1) Red potato: Basic carbohydrate that can be used in a huge number of ways.
2) Turnips: A good alternative to potatoes in some dishes, and to break the monotony of potatoes. Also produces an excellent cooked green. (And as a good green, as much as like spinach, I do not have to grow a separate cooked green.)
3) Corn: Hopi Blue Corn - The harder huruskwapu strain variety - Do a bit of research. One of the Three Sisters, great for no irrigation planting. (might add a popcorn, too)
4) Beans: My preference is Great Northern beans for soup beans/pot of beans, and for use in other dishes as an additive or stretcher since they are mild tasting. And small red beans for 'chili beans' (similar to Ranch Style brand beans), actual chili, and other 'Mexican' and 'Southwest' dishes such as refried beans.
5) Wheat: If I can cheat just a little, I would have at least two, and probably four types. Hard red winter for sure, soft white for sure, with soft red winter third, and durum as the fourth, if possible.
Without a separate greens needed, nor a squash, I would add the following two:
6) Onion: A yellow sweet onion. I like the milder, sweeter flavor. If possible, Vidalia, though I do not know its genetics.
7) Melons: Muskmelons for sure, with watermelons, as well, if possible. Something sweet. Muskmelons are a great addition to breakfasts, and watermelon anytime in the summer.
And since I do not agree with the '7', here are my additions:
Carrots: Part of my 'soup & stew' garden (along with potatoes, onions, and corn, and a couple more below), great as a side dish (honey ginger carrots - oh my), and for carrot crème pie during the holidays (much better and prettier than pumpkin and available all year round) (orange are best for pies, but one of the other heritage types of various colors would be good, too.)
9) Celery: Part of the soup & stew garden. Also great snack, alone and with peanut butter or cream cheese, and such.
10) Sweet peas: Part of the soup & stew garden. Also great side dish, in cold salads (though I do not like this type of dish), and other dishes.
And honorable mention:
11) Cucumbers
12) Tomatoes
13) Lentils
14) Oats
This is not including the many perennials, trees, bushes, and other plants that you plant once and harvest for years.
Just my opinion.