Even though it's tempting, you can't eat all your meals at a restaurant. Well, I guess you can. But if you're spending an extended period of time here, you probably will want to make your own food at some point, at least in part because there are very few places where you will find anything for breakfast aside from a medialuna (croissant) and coffee.
Your major grocery stores include Disco and Carrefour, among others. Disco regularly tends to be more expensive with less selection than Carrefour, so I lean toward the Carrefour. I go here for eggs, toilet paper, tortillas, vanilla, cleaning products, wine (the selection is enormous), and little else these days. It's summertime now, and with so many porteños vacationing out of town, it´s possible to check out without a long wait in line. During the winter, when I first starting shopping here, I experienced waits of up to an hour. It was horrible. This is what made me start looking outside the grocery store for my kitchen needs.
If you're a one-stop shopper, you can get most of what you'll need at these big stores -- but if you're a bargain shopper like me, you won't want to.
The verdulerias -- vegetable markets -- are consistently cheaper than the store, and they're everywhere. I pass three of them on my walk to the Carrefour, and there are a couple more in any other direction. I buy all my fruit and vegetables here.
The prices at these stores vary randomly: for example, on the corner, cherries are AR$15 for half of a kilo. Down the block, they're AR$20 for a fourth of a kilo! You won't always find such wide variance, but on berries of all kinds I have noticed differences, so I check all the nearby places before making my berry purchase.
These markets also tend to to carry eggs, mushrooms, fresh cilantro and mint, and sometimes bottled drinks. They carry what's in season and what's available, so occasionally you might get there and discover they have no broccoli or something. I base my cooking on what I find, rather than planning a menu and shopping to match it.
It can be hard to find hot peppers like jalepeños, but when I do find them, it's at a verduleria.
The fresh-baked bread at the bakery costs about the same as the packaged loaves in the store, so when I want bread, I go straight to the bakery and choose a wholesome loaf.
Rice, beans, nuts, granola, dried fruit, spices, chocolate chips, and much, much more can be purchased in bulk at New Garden, which has several locations throughout the city. Most products here are cheaper than in the grocery stores. They also carry various sauces and condiments, noodles, cookies and sweets, natural soaps and cosmetics, and honey. I have found that sauces -- like soy and Tabasco -- are a little cheaper at the grocery store, but it varies. I shop here about three times per week. I love it.
Grandiet, another store with several locations, also has some nuts, spices, and granola in bulk, but the big attraction here is the dried fruit: kiwi, melon, pineapple, grapefruit, papaya, mango, apricots, and more. Melon and kiwi are my favorite, and stopping here is an absolute treat. They also carry other nutritional products.
For empanadas, skip the grocery store version and go straight to one of the empanada shops. They offer more variety and the products are fresh and delicious. Many places will warm them up for you if you want to eat right away.
Cooking in another country can be a challenge if you can't find the ingredients you're used to, but if you shop around you will usually be able to find sufficient substitutes, at least -- and you´ll probably encounter a few new favorite foods.