A costly grocery mistake may happen before a shopper walks through the doors, according to cookbook author and content creator Jenn Lueke. Her warning focuses not on a particular product, but on starting the week without a plan.

Lueke, who is based in Boston and wrote "Don't Think About Dinner," identified the central problem in an interview with Fox News Digital. "The No. 1 biggest mistake is just not taking the time to plan ahead," she said.

In practical terms, planning means making a grocery list and deciding what to cook during the coming week. Lueke said that preparation can help shoppers save money while also reducing stress about meals.

Another possible source of overspending is the pressure to serve a different, impressive dinner every night. Instead, home cooks can return to familiar meals and adjust them using ingredients they already have.

Social media can provide inspiration, but it does not have to dictate a completely new menu every evening. Lueke, known online as Jenn Eats Goood, encourages cooks to make repeated meals part of their routine.

"You really can repeat meals," she said. Lueke added that a "base recipe" can be changed according to the season or adapted to use whatever is currently available in the freezer.

One example from her cookbook is a chicken thighs and rice dish prepared in one pot. Cooks can replace the protein or add seasonal ingredients, including squash in the fall and asparagus and peas in the spring.

Other flexible starting points include a meal served in a bowl or a vegetable frittata. Lueke said these options can help cooks use food that is approaching the point when it will go bad.

Keeping dependable ingredients in the pantry and freezer can create more possibilities during the week. Lueke recommends staples such as canned beans, rice, pasta and quinoa for building multiple meals.

Those pantry items can be bought in bulk or purchased when they are on sale. Frozen proteins can also reduce the need for shoppers to make grocery trips every week, according to Lueke.

For people trying to make a $50 to $75 grocery trip go further, Lueke suggests adding hearty, lower cost produce to meals. Her examples include carrots, onions, potatoes and sweet potatoes.

She also recommends affordable protein options such as chicken thighs, tofu and chickpeas. Combining these choices with pantry and freezer staples can give cooks several ways to prepare meals during the week.

Getting more than one use from the same ingredient is another part of Lueke's approach. If a recipe uses only some of a can of artichokes, she recommends putting the remainder into another meal.

Spice blends and homemade sauces can also give the same protein different flavors. This allows shoppers to prepare one ingredient in multiple ways rather than treating each dinner as a completely separate project.

"The biggest thing is having that plan, but also using one ingredient in more than one way, if you can," Lueke said. Her advice centers on planning before shopping, selecting adaptable foods and finding additional uses for ingredients already purchased.