There are several pantry staples that anyone cooking, whether on a budget or not, must have in their home. If you have none of these things then yes this will seem like a bit of a pricey jaunt to the supermarket but think of it as start up cost. Once you have these staples, you won't need to buy them for a while and you'll save TONS of money long term.
Olive Oil: I prefer the brand Filippo Berio for two reasons. 1. It's what we cooked with growing up. If it's good enough for my sicilian father it's good enough for me. 2. It's available at most chain grocery stores and it often goes on sale. Also the bigger the container the better the price per ounce. This is a good item to buy bulk as it doesn't go bad and you'll use a little bit almost every day.
Vinegar: Balsamic, Red Wine, White, and Apple Cider. Each variety has a distinct flavor and you'll find so many delicious ways to use them you'll never want to buy bottled dressing or marinades again. A lot of foodies will insist on only high quality varieties but if you don't feel like splurging that's ok. I find the inexpensive stuff still tastes fresh and delicious.
Spices: Sea Salt and whole peppercorns in a grinder. These are non-negotiable and extremely inexpensive adjustments to your cupboard. Even people who don't cook usually have parsely oregano and basil for some reason or another. Garlic and onion powders are also common as is crushed red pepper. I like to use fresh whenever possible but dried has its place too. In addition to the above, cumin, ginger, cinnamon, mustard and paprika are always in my cupboard. There are lots of others I like to use, but these are the essentials. Bargain tip: there's a national brand out there, we'll call it Shmicormickk, that kind of has a monopoly on spices in most major grocery stores. Unless you absolutely must, don't buy your spices from them. They're overpriced. If you go a few aisles over you'll often find a better price on spices in the organic section and/or in the ethnic foods sections, believe it or not (check the price per ounce to be sure). Alternatively pharmacy chains and other off the beaten path grocery distributers have staple spices, usually for around $1.
Baking supplies: Flour, Sugar, Baking Powder, Baking Soda, Cocoa Powder, Yeast
In the Crisper: Onions, Garlic. I prefer fresh, not the jarred stuff but if you're strongly averse to the extra 20 seconds it takes to crush a garlic clove go ahead and buy the jar.
In the pantry: potatoes (yellow/white and sweet) canned beans, all varieties, applesauce, low sodium chicken, vegetable, and beef stock, rice (brown and white) whole wheat pasta, whole wheat cous cous, canned tomatoes (diced, crushed and peeled varietes)
