Are you under the impression that families are going to the grocery store every day and trying to eat everything within 48 hours of picking it up from the store? No, people are buying the week's worth of stuff and might not be getting to actually cooking it until 6 days later.

Buy a week's worth of food, with each perishable item in quantities small enough to go into a few meals per week, out of the 21 meals you'll be eating that week.

Fresh vegetables and fruit last a week or two. Fresh meat lasts a week. Eggs last a few weeks. Most dairy products last a week or two.

Make meals out of a combination of fresh ingredients, dry goods (pasta, rice, beans, breads), canned/preserved foods/sauces/condiments, frozen foods. With basically one perishable feature ingredient per dinner, it doesn't take that much planning to feed yourself for maybe 10-25% as much as it costs from takeout or restaurants. Even if your food waste is double as a single person, that's still 20-50% the cost.