Actually, you can carry on if you have a connection and you buy at the duty free store in the gate area after security. The duty free store seal your purchases in a special bag with your receipt . At your connection, security will hand-check your purchase by opening the bag, inspecting the bottles, and then resealing the bag with special TSA-marked tape.

I just went through this process last month on my way back from SXM connecting in Atlanta and last year connecting in Ft. Lauderdale on the way back from Havana. Each time, it added maybe 2 minutes total to the time it took to get back through security for my connecting flight.

The duty-free store in PJIA is small right now, but it had what I was looking for: Havana Club rum and Ma Doudou (banana/vanilla - which reminds me of the island when I'm back home).