How much wine/balsamic vinegar can I bring back to the USA?

Yes it must be in checked baggage. Vinegar is not an issue. The alcohol you can bring back as much as you want, you just have to declare at customs in the US, how much you are bringing in, and be prepared to pay duty (tax) on it. You are allowed one liter (about 1.33 of a normal wine bottle) duty-free. Some people confuse that as being allowed only one bottle, but you can bring back more, just have to declare it on entry. Often they will just wave you through.

Packing is an issue, especially with soft-sided luggage. I use these plastic bubble wrap protectors (WineSkins, but there are other brands you can get here) for bottles, but also have gotten by with wrapping tightly in clothes and socks, etc. Too many bottles and they will bang against each other.

stan is correct - you can bring as much as you want.

If you're over your duty-free allowance for the wine, the customs agent will determine whether s/he believes the amount you have is for personal use (vs importing to resell) and whether or not you will pay duty on the excess.

You'd be hard pressed to bring so much back they'll get suspicious about the amount (because you'd pay exhorbitant excess baggage fees making it commercially non-viable :D ).

In our many trips I believe we've always brought back more than our duty-free allowance of whisky. We've declared it faithfully and accurately every time and haven't yet had to pay duty. The customs agents have complete discretion in that and I've always found them to be uninterested in making us pay duty.

YMMV, of course! But it helps to be honest, factual, pleasant and mentally prepared to pay any duty required.

You might consider sending it back through Mailboxes Etc., they will wrap it carefully for you. I usually send back a box with olive oil, balsamic vinegar, wine (or have the wine sent directly from the vendor). Regardless of whether you carry it or ship it, you must declare it.

I have obtained a wine shipping box from a winery, purchased a couple of bottles from a variety of wineries and filled up the box. I am referring to the heavy box where bottles lay flat and you place the protective layers on top. We book our flights using a frequent flier credit card or use miles and we get no charge for luggage. We then check our wine box as luggage and pay nothing. (I pack light and use a carry-on and may put a few things in my wife's larger suitcase). Even if you have to pay $50 for luggage, this is usually much cheaper than having the winery ship it to you. I have used this plan in the US, France, and Italy. the big benefit is that you can pick a few bottles from multiple wineries and are not limited to the one that does the shipping. I have also used the bubble wrap wine skins when I have only brought back one or two bottles.

Daughter, who lives in Italy, brings back 6-8 bottles of wine. SAVe the receipts for all wine purchased. The amount you will be taxed on entry depends on the $ value. Most Italian table wines found in grocery stores are very good and less expensive.

You might also look at the Crema Balsimico, more of a glasse. Comes in smaller plastic containers so you won't be adding too much weight vs the vinegar.

I have the wineries ship cases back to the states. Shipping cost is usually around 100 euro back to the US. Well worth it if you find a wine you really love and get a case of it.

If you choose to ship wine instead of bring with your checked luggage, be very careful with your local alcohol laws. Some states are more restrictive than others.

I've never had to pay duty on alcohol. As an earlier poster mentioned, you can't possibly bring back enough in your checked luggage to make it worthwhile for the customs agent to charge a duty tax.

I assume you are thinking of bringing back specialty wines, say from a winery? Because you'd be amazed at what you can find in the US. Many wineries will ship and that saves you from lugging bottles around on your trip and flight home.

You are correct, no liquids like this can go in your carry on, and you can't just put these items in a box or bag and carry on the plane. You will either have to pack in luggage and check (I know that Lufthasa charges $100 each way for an extra checked bag) or have it shipped. Shipping isn't cheap, and for me, it's not worth the additional expense to bring back this type of item. Unless it's an amazing product that I can't live without!

Thank you for all your great answers. 4 more days and we are in the air to Milan

As much as you want. You just have to pay for the shippine (100+ per case Euro)