I’m a bit confused then… what exactly do you propose the average American should put in their sandwiches—your suggestion—at a $40/mo budget? Eggs and lentils?
Moreover—can you put beans, rice, eggs, and mixed veggies in a sandwich? Because a sandwich was one of OP’s “$40/mo” suggestions. A food budget where a simple ham and cheese sandwich is an unimaginable luxury is ridiculous to propose as a reasonable target.
Not to mention the spoilage that goes on. The rice and beans can keep long-term, but you'll need to do logistics on chicken, tortillas etc to keep fresh ones in the pipeline without wasting any, which you can't afford either.
Look, I've had food boxes before. The food box is an amazing wondrous bit of charity where you can get a ton of free food just for asking. There's cereal, I've gotten big hunks of frozen meat, dry beans and rice, I've gotten bits of candy and such, lots of staples, powdered milk, canned chickpeas and spinach and you-name-it.
However the food boxes only go so far. They won't cook the meals for you. They won't give you the utensils, pots and pans. You don't get any fats, oils, herbs, spices, or seasonings. they won't tell you which ingredients combine in a flavorful way. You don't get any recipes that use these ingredients and don't call for something you don't have.
Now you boil some water, throw in some beans and rice plain, and cook until soft. Go ahead, throw in some string beans for vitamins, and some kind of protein. Spoil yourself! Then try to choke that down in the absence of salt, butter, or anything that might impart flavor. How long until you're going to just kill yourself?
You realize that there are people who are homeless and who live in areas that don't have any support systems for homelessness (e.g. homeless shelters), right?
But of course, there will always be people falling through any cracks. That does not mean that the original piece of advice isn't sound, though.
You have proposed that a homeless person obtain a phone, find a library that'll mail books, obtain a mailbox, have a book mailed to them, presumably pay for return postage, all so they can obtain recipes to cook on a stove they don't have with utensils they likely lack with ingredients they can't afford.
Homeless people aren't in that situation because they needed someone to write down "how to make rice in a pot", nor are they likely to have discretionary income for your proposals.
And I feel like you do not understand that the average American is not homeless.
If you are homeless you are not going to be a person who is spending >$40/mo for food and needing a cook book to make cheap food interesting to eat. You will just buy cheap food until you bootstrap yourself back to a house and a stable job.
People who spend >$40 per month on food who live 40 miles away from the nearest library.