In most cases, travelers entering the U.S. are eligible for an $800 exemption if returning from any country other than a U.S. insular possession. This eligibility applies only to items that you actually have in your possession. Items that you mail home to yourself follow these duty-free guidelines [source: U.S. Customs and Border Protection]:
• If purchased from an insular possession, up to $1,600 in goods may be mailed duty-free. The amount you mail counts as part of your $1,600 duty-free total.
• If purchased from a Caribbean Basin Initiative country, up to $800 in goods may be mailed duty-free. The amount you mail counts as part of your $800 duty-free total.
• To get this benefit, you'll need to ask the merchant to hold the item. Next, fill out Form 255 when you clear customs, listing the value of the item. Then, send a copy of the form to the overseas merchant so he can mail you the item, with the form attached in an envelope to the outside of the package.
• For other countries (or if the package has already been mailed), you'll pay duty to the U.S. post office or freight service, as needed, when the item is shipped to you.
Tobacco -- Your $800 duty-free exemption may include up to 200 cigarettes and up to 100 cigars. If you bring more than that, you'll have to pay duty on them, even if you haven't gone over your total exemption. (You may also have to pay state or local taxes on tobacco products) [source: U.S. Customs and Border Protection].
Federal laws states that you may not bring back cigarettes that you purchased in another country if they were manufactured in the United States for export purposes. That definition includes most cigarettes you would find sold in stores; an exception (a rare one) might be cigarettes someone purchased in the United States, took to another country and tried to sell, Mann says. You'll know the difference because cigarettes made for export purposes don't generally bear the Surgeon General's Warning label or tobacco seal; cigarettes purchased in the U.S. must have these stamps. All tobacco products made in Cuba are prohibited [sources: U.S. Customs and Border Protection, U.S. Customs and Border Protection].
Alcohol -- You are allowed to bring in 1 liter (33.8 fluid ounces) of an alcoholic beverage (liquor, beer, wine) as part of your duty-free exemption if you are 21 or older and the beverage is a gift or for your own use. (This allowance is subject to state laws -- check yours before you leave on your trip. If returning from an eligible Caribbean Basin country, you are allowed 2 liters (68 fluid ounces) duty-free, as long as one of the bottles was produced in the country. If returning from a U.S. insular possession, such as the U.S. Virgin Islands, American Samoa or Guam, you can carry up to 5 liters (169 fluid ounces) of alcohol across the border as part of your $1,600 duty-free exemption, as long as 1 liter was produced in a possession [source: U.S. Customs and Border Protection].
If you want to bring back more for your personal use -- unusually large amounts raise red flags about your intentions for the product -- you can. But you will be charged duty and Internal Revenue Service tax. (The U.S. Customs and Border Protection enforces these laws on behalf of the Bureau of Alcohol, Tobacco, Firearms and Explosives. This means they are within their rights to decide that these products are being brought in for commercial purposes and to hold the alcohol until you obtain a permit to import it.) Finally, importation of absinthe, a potent green liqueur flavored with European wormwood, or any other liquor or liqueur containing an excess of Artemisia absinthium (wormwood) is prohibited [source: U.S. Customs and Border Protection].
Firearms -- Under Federal Aviation Agency (FAA) regulations, no U.S. commercial airline allows firearms in its airplane cabins except in the possession of law enforcement officers. ATF also regulates and restricts firearms and ammunition and approves all import deals involving weapons and ammunition, which must be arranged by a certified arms dealer. There are some exceptions for antique firearms, which are outlined in Chapter 93 of the Harmonized Tariff Schedule [source: U.S. Customs and Border Protection].