There are some things that I try to always have on hand in my kitchen. Sometimes there are no exciting sales, or I find myself cooking for guests on short notice. By keeping a few things constantly stocked, I give myself some flexibility to make a decent variety of dishes with whatever other random ingredients are lying around. Some of these are generally inexpensive, and others I buy piles of when they're on sale. They also tend to have decent shelf-lives.
* Mirepoix is the fancy French word for chopped carrots, onions, and celery. These are three good veggies to have around, and are commonly tossed into soups, salads, stews, roasts, and stock. Carrots and celery are also good alone as a snack. Onions are very versatile and fit in fresh or sauteed with meats or grains.
* Potatoes are easy to bake, roast, boil, or microwave, and go well with most meats. Sweet potatoes are even better.
* Eggs are versatile and necessary for most baking.
* General baking supplies: flour, sugar, baking soda, baking powder, oils, butter, salt
My pantry is full of other things, canned veggies, dry beans, pasta, tuna, but I don't consider those essential, and I do not necessarily rush to replace them when they run out. I do not even have milk most of the time because of its relatively short lifespan. I usually have some chicken breasts in the freezer, but not always. Between my staples and whatever else is lying around, I am generally equipped to feed people easily.