Also tip when you buy duty free in Mexico or Caribbean ensure that they pack it into tamper proof sealed bags, last couple times they tried to pack it into a normal bag and then zip tie it .. that doesn't fly if you have to go through security. But usual when you ask for the tamper proof sealed bags, they do have them.

Last AA flight from Caribbean they were even making announcements about putting your duty free into checked luggage before re-entering security. Same announcement by TSA. But I had no problems going through with the correct bags.