The woman who wrote the book on eating for $4 a day shares her best tip to save money on food

Leanne Brown wrote the book on eating well for less.

Her cookbook, "Good and Cheap: Eat Well on $4 a Day" has been downloaded more than 900,000 times, and over 71,000 updated hard copies have been given or sold at a discount to help people in need. For each copy of her New York Times bestseller sold, she donates a copy to people who might not otherwise have access.

Brown originally wrote the book as her thesis project for her Master's degree in food studies at New York University. She intended it to be a resource for Americans who receive SNAP benefits - Supplemental Nutrition Assistance Program - which is the official name for the federal government assistance program often known as food stamps. Under SNAP, recipients are given an average of $4 per person, per day to spend on food.

She has many tips to help people get smart about eating well on a budget,but her top tip, she tells Business Insider, is to buy foods that can be used in multiple meals.

"I say buy eggs, because it's one of the most flexible ingredients that exist," she explains. "You can get home from work and have them on the table in a few minutes. They go with everything: If you only have soy sauce and really withered scallions, if you have half a withered tomato, you can chuck that in there. You can bake with them, make beautiful quiches, or cook them in sauces so they're more like a dinner."

Other specific foods she relies on include dried beans, fruits, and plain yogurt. "It's really about buying things that you have more than one use for," she says. "If you like yogurt, don't get the little single-serving cherry yogurt. It can only ever be a little cherry yogurt. If you get the tub of plain yogurt, it can be plain yogurt or something really different. If you're into baking, get flour and baking soda - these things to allow you to bake, whereas if you just get pancake mix, you can only ever get pancakes."

"That's the ultimate tip," she shares. "Get your pantry kitted out so you can go to the store and get seasonal fruits and vegetables, and come home and make all kinds of great things and be inspired by your favorite cuisine of the week."