Ipods in Argentina cost around double what they do in the USA.
Same thing with laptops, or small digital cameras.
Everybody is different, in terms of what they like, what they cant live without, and their tastes.
I never eat peanut butter, so the lack of it in BA doesnt bother me at all.
But I am a big fan of Good Earth sweet and spicy tea, and always bring down a couple of boxes when I come, as the local tea selection is very limited.
I bring a bottle of good whisky or bourbon with me- again, argentine selection is limited, and expensive.
I could not find a good small grater in BA to save my life- and I use one all the time for zesting, grating ginger, and fine grating cheese into omelettes. So I brought a $3 model from the USA.
I bring down CD's of american music, as imported CD's here can be very pricey- and trade them with argentinian friends for local bands, which sell their CDs for ten bucks or so. Lots of great local music here.
I dont have any particular fetishes about brands of personal grooming products, so I am fine with local production- but if you do, bring it.
In general, global mass market goods are USUALLY, but not always available. But at a higher price. For most products, be they food, cosmetics, or hardware, the local stuff is cheaper in price, about ten years behind in trendyness, and and lower in quality. So if you are a stickler for a certain brand of lipstick or shampoo, stock up.
However, I find it quite interesting to live locally, where ever I go. Nope, you cant get Barq's root beer, or Jones Soda in Buenos Aires. So I drink Terma- local, not very sweet, herbal soft drinks that really hit the spot, with a bit of ice, on hot argentine days. You cant get a decent donut, or a bagel. The tacos they sell are pathetic. But if you eat the local food, you find all kinds of interesting stuff that they dont have in the USA. Roquefort and corn empanadas, Bondiola sandwiches, french fries with onions and garlic, alfajores, pumpkin tartas, fuggazetta y faina, pastel de papas- there are all kinds of great discoveries to be made.
Same thing with shoes, or clothes. Nike shoes are very expensive here- but you can get a really cool pair of Carpincho leather loafers for a quarter the price of imported Nikes. Local designers make interesting stuff, cheap, or you can buy imported euro styles for triple what you are used to paying. Leather goods in general are higher quality, and can be reasonable if you shop around. Virtually all leather in the USA today, coats to sofas, is chinese pigskin. Argentine cow leather is much nicer, and cheaper.
The shoe industry in Argentina is a gem. Small designers can actually get a dozen pairs of shoes made, in a custom design. This small scale is unheard of in the USA, or in europe for less than 500 Euros or so. But all over BA, you find small boutiques who have womens shoes for 200 to 400 pesos that are totally unique to that store. We have had probably ten different US women friends down- none has left with less than 3 to 5 pairs of new shoes.
A lot of the best deals here are antiques. My wife bought a pair of art deco, 80 year old, 1/4 carat diamond earrings at the San Telmo flea market last year, generally considered to be the most expensive flea market- for around a hundred bucks. Got em appraised in the USA later, they said probably $400 to $600 there. Vintage clothes are rarer, but old watches, jewelry, books, fur coats, knickknacks and fountain pens, advertising novelties, furniture and seltzer bottles- all kinds of real things made the old fashioned way are for sale here for a fraction of US antique store prices.
I have an apartment, so I can buy furniture- and the furniture pickings are marvelous- amazing stuff, very cheap.
My advice is bring empty bags. Thats what I always need, when I am returning to the USA, as I have bought so much stuff.