Help me come up with a cost efficient shopping plan for my family of four.

There is no one shopping plan for any family of four; there are simply too many variables and constraints to consider - and too large a data set - to consider and make a recommendation for a family of four without further context. Some of these variables would include:
- Household income and net worth
- Cost of living
- Living and family arrangements
- Medical conditions

However, there are some basic guidelines which can inform a high percentage of households which rank among the median or most common scenarios. For example, for a family of four in the United States with median income and net worth:

- Set realistic budget and time numbers per month and document
- Document prices for low-cost household staples such as beans, rice, bread, milk, eggs, butter, oil, seasonings in your area by store
- Repeat for fresh fruit and vegetables, meat and fish, ready-to-eat foods, and other items for your family's diet
- Create a shopping list and mark down on your calendar when you will buy each item

There's a first step toward a cost efficient shopping plan for a family of four.