Foods/ingredients to keep in stock in the kitchen?

It seems my fiancé and I always run out of food at home! We go shopping twice a month to the grocery, but buy more convenient meals to suit our busy work schedules. When I see other kitchens at our friend’s houses, they are always so well stocked and they can whip a good meal up without going to the store.

What are some key ingredients or foods I can keep in the kitchen so we will be more stocked?

Thanks in advance!
Wow these answers so far are all fantastic!

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