The result is that there is almost no reason to buy anything at all while you are actually traveling EXCEPT for two kids of things: 1) those few, amazing, precious, magical things that truly can only be bought on location; and 2) those things that are much, much cheaper or better on location. And here they are:
If you are American traveling to Italy, don't go home without:
1) CHEAPER: Caffè Vergnano (my favorite, from Torino) or another really yummy coffee that is totally ordinary in Italy and totally costs a fortune in America. It's worth buying a dozen at 3€ a package and filling up your stash at home, rather than paying $10 a package. Keep in mind that espresso is not a type of coffee, it's just the way the beans are ground, so you can brew Italian coffee in your normal coffee pot if you don't want to make it Italian style, but still want a nice smooth java...
2) CAN'T GET IT: Your broken stuff from home, all shiny and new. The cobblers, jewellers, and tailors are twice as good and half as expensive in Italy as the best rated ones I could find when I was living in New York City. Drop off all your shoes that need re-soling, watches that need repair, purses that need new handles, clothes that need taking in, pants that need hemming, and jewellery that needs fixing when you get here, and pick it all up before you go home.
3) CHEAPER: If you're the kind of person who spends a lot on business suits (which I am not), and you will be in Italy for a few weeks, consider having one made. You can still find a few fine tailors for very affordable prices, and the quality is really unbeatable.
4) CHEAPER/CAN'T GET IT: The same goes for having shoes made. If you have difficulty getting shoes that fit comfortably, the quality-price relationship here really makes the custom option worthwhile. At any rate silk ties and fine shirts and shoes for work purposes are much cheaper and worth purchasing in Italy.
5) CHEAPER: Parmigiano Reggiano. This ain't no parmesan. It's also not what I found labeled "Parmigiano Reggiano" in our supermarket in Indiana (I'm still not sure what that was...) You should bring an extra suitcase for this stuff and buy the biggest block you can. Its success is guaranteed: whether you eat it by the chunk or grate it onto your pasta (or heck, finish it on the plane) this is one purchase you will never regret. Remember that it MUST BE VACUUM SEALED to bring across the border. Don't try to bring prosciutto, salami, or mushrooms home, or border control will make you cry as they once made my husband cry (well, almost). If you don't like to eat cheese, you could just use it as insurance: when my great-grandfather immigrated to the Bronx in the early 1900s, he brought wheels of this stuff just in case the bottom went out of the economy. Some people have gold bars under their mattress, my family had a room full of cheese...
6) CAN'T GET IT: Big onesies and wool stuff for kids. Italians are obsessed with defending themselves from "hits of air," which might invade their clothes and afflict them with all sorts of maladies we don't seem to have in the US. One of the nice results of this paranoia for us visiting parents is that they make baby onesies in sizes that fit children up to four years old. And if you like keeping your kids' tummies covered like I do (to, you know, protect them from hits of air), then these are very convenient. And the cotton clothing in Italy tends to be very nice quality. You can also still find some wool clothing for babies and little kids, which is warmer and less bulky than cotton winter clothes and has become really hard to find in the States.
And actually, wool and cotton stuff for adults is great in Italy, too. Go into one of those ugly little storefronts with no sign, but with long johns, socks, and pajamas pinned up in the tiny window and stock up on pure cotton and wool socks, undershirts, and long johns. No hits of air here!
7) CAN'T GET IT. Napisan. I don't know why this doesn't exist in America, but it's amazing. It's a laundry additive that doesn't bleach your clothes, but eliminates germs. For things that can't be washed in hot water and aren't white, it's a must! Make sure it has the approval of the "presidio medico chirurgo" on it, with the red cross symbol - that's the one that is certified to eliminate germs.
8) CHEAPER. THIS THING. Simply the best. Better than all the rest. (Since I drafted this post, the Bialetti Tuttocrema became available on American Amazon. It costs more than it does in Italy, but who can put a price on happiness, I ask you?)
9) CHEAPER/CAN'T GET IT. Chocolate. Get a local one and stock up! Put this in your extra suitcase with the parmigiano. If chocolate is not your thing, another artisan ("artigianale") desert option is really worthwhile. Generally the especially good stuff has simple and local ingredients, and the kind of stuff varies by region (e.g. lots of things with hazelnut and chocolate in the north; lots of things with citrus, pistachio, and almond in the south). Although often these things are imported to specialty stores in the US, here they're a quarter the cost and you can pick them up at any supermarket.
10) CHEAPER. Wine. Make sure it says d.o.c. on the label. Six euros will get you a very nice wine. My favorite is a red wine called "dolcetto." And don't forget that bubbly prosecco makes everything better. If you happen to be in wine country (which you very likely are), go to the place that makes the local d.o.c. and get your bottles for as cheaply as 2 or 3 euros there. Maybe you're going to need another suitcase...
11) CANT GET IT. I LOVE Italian "amari," after-dinner drinks that are apparently called "digestives" in English by English speakers who take constitutionals, wear smoking jackets, and say things like petit-four. You can get some of them in the States, for a high price, but not my favorite one, which is an Alpine digestive called Braulio. On your way home you can always touch down in England and find yourself a smoking jacket...
12) CAN'T GET IT/CHEAPER. Tuscano cigars. Medium-width, long cigars to be cut in half and smoked with a friend. Too mild for a strong praise; too tasty for a mild praise... Don't inhale, people.
13) CHEAPER. Something made with leather, linen, or embroidery. These include: bed sheets, leather gloves, shoes and boots, curtains, table linens, purses, and clothes. Go into an off-brand store that has these items in the window. The prices will be higher than getting polyester or plastic equivalents, but will be significantly lower than getting comparable items in the States.
14) EASIER TO GET. Unlocked by law, smartphones that are unattached to a particular phone plan are widely available in Italy.
Italian expat readers, what do you bring back to America when you visit Italy? Add your own must-haves in comments!