International airports usually feature duty-free shops that sell liquors, perfumes and other luxury items to outbound travelers. These items are called "duty-free" because travelers do not have to pay customs taxes, or duties, on their purchases because the travelers are taking these goods out of the country.
TSA Rules and Liquid Duty-Free Purchases
The Transportation Security Administration (TSA) rigorously enforces its regulations pertaining to transportation of liquids, gels and aerosols in carry-on baggage.
Any item containing more than three ounces (100 ml) of liquid, aerosol or gel must be transported in checked baggage once you arrive in the US.
This means that you can purchase duty-free liquid items (perfume, liquor, etc.) at a duty-free shop outside the US and put them in your carry-on baggage for the international leg of your trip only. If you are changing planes in the US, you will need to put any liquid or gel duty-free items in containers that hold more than three ounces (100 ml) in your checked baggage after you clear customs at your point of entry. However, if you buy the items at a duty-free shop outside the US, they are in transparent containers and the shop has packaged the bottles in a tamper-evident, secure bag, you can keep them in your carry-on bag all the way to your US destination.The TSA changed this rule to permit use of secure, tamper-evident bags in August 2014.
For example, a traveler flying from Cancún, Mexico, to Baltimore, Maryland via Atlanta's Hartsfield-Jackson International Airport could purchase duty-free items in the Cancún International Airport's shopping area and take these items to Atlanta in a carry-on bag.
Once that passenger clears customs in Atlanta, any liquid, gel or aerosol items larger than three ounces will need to be placed in a checked bag before boarding the flight to Baltimore unless the bag is secure and tamper-evident. Otherwise, TSA officials will confiscate the bottles.
How to Pack Liquid Items and Place Them in Your Checked Baggage
Placing bottles of duty-free liquor or perfume in your checked baggage could be risky, for obvious reasons.
However, planning ahead and packing a few useful items can help you minimize the risk of having a bottle break inside your checked bag.
Bring wrapping materials, such as packing tape and plastic grocery bags, to secure breakable bottles. Consider packing an old towel; you can use it to wrap wine, perfume or liquor bottles. Once you have wrapped the bottles, put them in the middle of your suitcase so that a direct blow to the outside of your bag will not break them. I normally place glass bottles in at least two plastic bags, wrap the bundle in a towel, place that bundle in yet another plastic bag, and pack it in the center of my largest suitcase.
Alternatively, you could purchase protective packaging, such as the WineSkin or BottleWise bag, before your trip. Use one of these commercial products, available at many US liquor stores and online, to seal your liquor bottles in cushioned plastic wrapping. I have used WineSkins with great success.